Just thinking what a Pulp-Roaring 20's Planescape would look like. Here are a few ideas.
1. In order to have the mob families arise on the planes like they did in that era there needs to be some business for them to control. By bussines I mean something illegal for them to smuggle, make and sell over the planes. PS doesn't really have a wide spread enough government to make such bans far reaching enough if you want mobsters racing across the outlands with huge supplies of liquer.
2. Solution: Make the upper planes and coorisponding areas of the outlands land under the control of one government. Perhaps put Prohibition from Elysium on over around the ring to the Gray Waste. What started out as a crusade of ideals and good intentions has spread far beyond what it can stand. If you want to go a little less then say the new order covers Acheron through Bytopia. I like the wider spread myself because it gives Law outwardly more power, thus the chaos of gangland can really erupt to restore the balance (Did someone mention Rilmani?).
3. Sigil may fall under either side of wet or dry. I like to have it with one side trying to enforce the laws while the other side thumbs their noses at it. Think of it as Sigcago?
4. The Astral -- Dry when the authorities are around in greater numbers than those who want it wet.
5. The Inner Planes -- Groups are trying to bring prohibition to the elementals, but the elementals are curios what this alcohol is, except for the fire ones they like the burning.
6. The Etherial -- Some try to make the strongholds of the fey dry…It's rather amusing to watch.
7. The Primes -- As always with Primes it is a case by case basis.
8. Technology. Steam, internal combustion, tommy guns, dynamite and electricity, need I really go on at this point?
9. The Far Realm and Lovecraftian ideas -- There truly are things that man and planar was just not meant to know… and those things are waking up.
10. Dark Continents: Three oceans have been discovered on the outlands each about 7 days travel from their nearest gatetown away from the spire. Strange reports of dark continents with unknown horrors are filtering back. Reports of riches of coarse are rushing back.
11. Nazis -- The ultimate baddies for pulpgames. It just wouldn't be the same without an evil well-educated empire making moves towards world and planar domination. These guys have taken over a confederation of Prime Worlds and are starting to make theirselves known on the planes, espousing the virtures of racial purity and other ideals. Note: This is an early Nazi era where their role is uncertain to the outside world. Even good people might susscribe to their ideas believing that the bad things they might or might not have heard are just fiction.
Hobgoblins. Maglubiyet's forces are temporarily winning in the constant wars of Acheron, and thus the goblins of the Prime are more powerful than ever. As they grow in power, they've sought out the advantages of civilization and technology to use against their Orcish enemies, and anyone with Orcish blood, and Orc sympathizers, and maybe a half-dozen other groups of "undesirables".
After all, it's pretty easy for most people to agree with getting rid of all Orcs, everywhere... and plenty of otherwise good people believe in killing orcs wherever they're found, even if they're just small Orc children. Of course, as the Hobgoblins' efforts branch out beyond their Orcish enemies, people will start to wonder when the slaughter will end...