Sigil/D20 Modern/D20 Future outlandish ideas

I'm thinking several stay the same.

Granted, I have not put a whole lot of work into thinking about how it affects each and every plane. See, while most modern RPG settings or even Sci/Fi ones take place in a universe much like our own, I've been playing around with the idea of taking existing ones and applying them. This adds a lot of factors to the mix including Gods, Planar beings, MAGIC! In D&D, which is what I run; there's also the fact that Spelljammers allow space travel long before you reach a Sci/Fi technology period.

I was running my universe under the idea that the Powers have always managed to keep things from reaching a point where mortals no longer needed them or considered them irrelevant. However, this project and curiosity stemmed from a series of journeys through time that an epic level party is taking. They've achieved epic spells that can carry them several centuries into the future or past (though this isn't done so much because of the inherent dangers) I buy into the alternate timeline theory which means traveling to the past can inadvertently change their present to the point where they don't want to risk it.

So far, as I developed my own world's future history, I determined that several deities tried to derail progress and then other newer deities arose such as a God of Progress with his Church of Civilization. I even mapped out a dark age that took place after an equivalent of the Modern Information Age where destructive deities allied with fiendish agents brought about nuclear wars to put the mortals of a few worlds back into lower progress levels.

I feel that the Planes themselves would be mostly unchanged at their core, though the settlements there would have the same technology that exists on material worlds. I imagine that as technology reduces a prime dweller's interest in putting in the work to learn magic, contact between the material worlds and the planes would begin to decline as less spellcasters reach the levels to plane travel, but then what happens in Sigil? I'm picturing a city crammed so tight that there are no longer streets but corridors and (subway) like systems running everywhere. New Factions arise including evolved versions of the old factions with some believing that the universe is heading for an inevitable apocalypse. The rising tide of data and information requires entire factions obsessed with discerning truth from deception. The Blood War begins to get massively bloody with the Baatezu creating weapons giving them a glimpse of eventual possible victory. Archons, Celestials, and other Upper Planar beings generally remain unchanged though they may even go as far as learning how to build defenses against massively devastating weapons just in case the lower planes resolve their so called eternal war. One big question is... In a Universe where mortals can create devices and gadgets to duplicate the abilities of magical creatures without raising tons of levels in Wizard or Cleric to do so; how do their beliefs shape the beings of the outer planes. Do they imagine even more powerful planar beings? Or do they merely imagine powerful beings able to do these things free of technology or device? hmmm, thinking as I'm writing...