It should be noted that in DC Comics the multiverse exists again, it's different than what it was like with Crisis On Infinite Earths, as some of those worlds don't exist anymore, some do, and there's an Earth-50 which is the home of the Authority, Stormwatch, WildCATS, Gen 13, etc.
They decided they wanted some of that complexity back again, even with the "other comic companies (that we purchased) stuff in other Earths" things they had going.
Much of the things from PS like the Blood War and Modron March could still exist under the new cosmology. The new cosmology is supposed to be more open, with a less defined planes, though it does make some things from the Great Wheel hard to work with at times.
PS also could still have the cosmology the way it was, and still work fine with 4e rules. Already I've seen hints that their making PHB Eladrins fit in FR, by continuing to call them Gold or Sun Elves.
Many of the 4e changes are usually in terms of things like monsters and races, and it's easy enough to fix those with a little work.
Other 4e changes like Paladins of any alignment, Rangers of any alignment (that's a 3e change), Warlords, and Warlocks (3.5e change) actually have things to add to PS with more options. Though it might result in certain NPCs getting retconned as different classes.
Option 3, for now: play the 2e fluff, with 3.5e mechanics and the PSCS from the fine folks here at planewalker, and worry about 4e if they ever put out interesting new fluff that makes me want to play in that meta-setting. :^)