Timeline

It seems there's a few key things that need to be decided. Offhand, these are:

• Earth year for breaking blockade
• Time since breaking blockade
• Year where Earth stops being real-world Earth
• Time after FW
• Timing of 'Mechanus reboot'
• Timing of Pandemonium's little change
• Discovery of Cyberspace as... um... a plane.
• Timing for major technological developments?
• Demihumans popping up (if used, that is)

Just out of curosity, what PL are you going to set the "Real" world 5, or 6?

PL 5: INFORMATION AGE
The Industrial Age relied on chemical power, but in the Information Age, computer technology and electronics rule supreme. Satellite information systems and the Internet connect the globe digitally. This Progress Level also sees the introduction of fission power and weapons reducing the importance of fossil fuels. The automobile replaces the locomotive as the common form of travel. The first steps toward space travel involve massive chemical rockets, unmanned probes and satellites, and short-term manned missions.
The technology of the era allows greater citizen participation in government. The emergence of international alliances begins to dissolve borders between nations. Corporations gather power and begin to threaten government authority. Technology has a greater effect on individual lifestyles than on society as a whole. Most weapons at this time are refined versions of Industrial Age equipment. Rifles, machine guns, and heavy howitzers are still used by the world’s soldiers. Computerized targeting systems and guided weapons make warfare much more precise and efficient. Strategic weapons, tested but never used, exhibit the species’ power to exterminate itself in minutes.
Humanity experienced its Information Age as anxious years full of minor crises. The tension gradually alleviates through the age, and as the era ends new superpowers form.

PL 6: FUSION AGE
The development of fusion power provides an efficient, nonexpendable energy source that almost obliterates the need for chemical fuel sources. Advanced space exploration and colonization become possible. Computers become even more accessible, reliable, and powerful, leading to the development of virtual systems and widespread access to the global Internet.
Slowly, society experiences another revolution as individual nations are replaced by world powers. Megacorporations number among these new superpowers as the line between the national citizen and corporate employee is rendered indistinct. Armed with the means to eradicate the entire species, the world powers keep conflicts to the level of skirmishing and posturing, and integration of the Information Age’s improvements proceed peacefully.
Scientific advanced in genetic engineering lead to artificial evolution and the first government- and corporate-sanctioned attempts to genetically manipulate human beings. Early results are encouraging, with the manifestation of positive and negative mutations in the species toward the end of the age. Scientists also perfect cloning technology, and the first human clones are created.
In the later years of this age, the first crude applications of gravity induction technology appear, in the form of civilian and military vehicles that can move through the air without using physical propulsion or consumption of fuel.
Chemical-powered explosives and firearms remain the weapons of choice; fusion technology can’t be effectively miniaturized for personal combat. Nevertheless, advanced chemistry and superconducting technology change the materials and capabilities of many weapons. True spaceships become possible, propelled by powerful fusion drives, but still require a reaction mass to traverse space.
The age sees the tenuous settlement of other planets and asteroids within the same star system.

Either way, it's good to figure out what kind of technology we're planning on using. Are we planning on using common real-world tech, bleeding edge tech, or near future tech?

It has serious implications on the kinds of plots that can develop. What does biotech look like? What does space travel look like? Have we encountered extra-terrestrials on the Prime? What are cutting-edge computers and robotics capable of? Is there any sort of meaningful AI?

Of course, with the bizarre effects of magic and planar travel, these questions could be a little less important-- material designed for the 1980s, as was mentioned earlier, could probably be used in the 2030s, and vice versa, without seeming out of place. (Or, at least, any more out of place than anything else.)

Of course. I'm merely firing off the questions in an attempt to get a dialog started-- since the answers to these questions will have a powerful influence on the setting's tone.

(That, and I've been trying to run a Planescape/Star*Drive crossover campaign for years, and the idea fascinates me.)

I am inclined to agree... though I'm forced to wonder what effect, exactly, the planes would have on technology. I can see perhaps the development of non-magical planar sextants, but I'm otherwise stumped. (Well, I do have a couple of ideas regarding using the Astral Plane to circumvent relativity, a la Dragonstar, but that would involve changing the tone of the setting considerably.)

Going in the reverse direction, however, I can easily see how modern beliefs and practices might change the planes... the banks of Hell are a very vivid image.

That seems like a natural place to start-- with expanding Earth's infrastructure throughout the planes as much as possible, adapting to planar physics which do not match up with our own. There could be several interesting adventures based around such efforts.

I'd gathered that. Strikes me as a lovely idea-- the Githyanki are a perfect Planescape blend of alien and familiar, and they fit well with our popular media images of extraterrestrials. I can imagine, after discovering that the Planes are shaped by belief, rampant speculation that the Githyanki were created by a century's worth of UFO abduction stories and ET invasion plots; and, of course, the Githyanki becoming very highly offended by such speculation.

Of course, this causes me to wonder if, even if we're avoiding extra-terrestrial Primes, the Fraal might not have a role to play after all.

If rare, such things might prove interesting, but I dislike intensely the idea of merging magic and technology, or worse, having magic-dependent technology, especially for inventions which would quickly become influential forces on society (like immersive cyberspace).

On the other hand, magic does provide new avenues for research into these fields, and I see no problem with cross-disciplinary exploration.

Why? It opens up such a vast field of research - and if they do become major features of society - well, its all meat for the grinder, more story hooks - as opposed to just 'Planescape with guns'.

Afterall, Earth forces are probably only incursing onto the planes in order to nick technology (magic) - at first it will be simply stuff like magically enhancing their firearms in order to fight the inevitable demon attacks, but as things move on (and more people discover the planes and get there on their own initiative) the fusion of everything seems inevitable...

Right, and wrong. Technology plays by the rules of where it's from, and its ability to work depends on how well it can play by the rules of where it is. Earth technology will work best under earth-like circumstances, but may function completely differently (or not at all) in Limbo.

Magic breaks some rules, but follows others. The more rules it breaks, the harder it is to use [spell levels]. In places where the rules are different, it is either more or less effective [planar traits].

Merging the two everywhere, all the time and in every way is exactly as likely to happen as a +5 enchantment on every rock on Avernus.

Sigil sits above the infinitely tall Spire. Impossible's not an obstacle.

My mental image of mixing magic and technology were specific elements of either being used to 'hack' around some limitations of the other.

For example, cyberspace constructs hack golem creation for programs with limited intelligence and awareness. On the other hand, you're not going to see an iPod of Fireball. Spellbooks recorded in an electronic format are reasonable, whereas PowerWordKill.exe isn't.

Spell trading would probably need some kind of special connection, in much the same way as scrolls and spellbooks need to be made out of special paper.

Machines programmed to make or use magic aren't going to happen. Select elements of machines programmed with magic or made to work with the aid of suitable enchantments, however, may be possible. Spells targeting machines are also likely.

I like this, if it's suitably rare-- the product of exceptional people trained in both disciplines. (Or even as a collaborative effort.) I don't mind the occasional technomagic artifact, or an adventure or two that revolves around some bizarre implentation of technomagic.

As long as it isn't a staple of the setting, a major theme, it's an intriguing concept.

Except that, given the planes exhibit different laws in different spots, technology has a locally factual basis. Those technological components further break down into their interactions with their surrounding environment, leading to further complications for the aspiring technomage. It follows that a technomage using some piece of technology from the Grey Waste, enhanced with magic on Elysium, would only really expect it to work 'properly' on the Outlands - and then, each component would be weaker than it otherwise would on its home plane.

[yes, you can assume that I liked the 2e system of degrading enchantments for distance from where items were made]

Beyond belief, the environment itself poses a hazard to some pieces of gadgetry. Some shiny technological toy from Mechanus will have extreme difficulties working in Limbo, for example.

It'd follow that any pieces of advanced technology that might be in a Gith city are engineered to *rely* on the surrounding chaos, or on Anarchs.

Cold is indeed another good one. The flipside to that, of course, is that a number of mechanical things run better hot.

I think Chaosium's love of detail comes from Lovecraft's writing style - get the normal things *perfect*, and the horrific details are so much more effective.

And your infectious asterisks make me *feel* like I'm playing Torment.