It suddenly hit me. What the heck would a crossover between the FMA anime and the FMA manga look like?!
The obvious way to do it would be to have anime!Ed at the end of the anime go through the gate, and appear in the manga-verse. Which means that Envy and Hohenheim would be appearing there too. Envy would obviously not become the snake-dragon thing, since alchemy in the other Amestris works just as well.
Two Envys. Now that is a rather scary thought. There's the chance they might hit it off, but on the other hand they might end up jealous of each other...in an out-and-out fight, who would win? I think the anime!homuns are in general harder to kill than the manga ones, especially for another homunculus, since only an alchemist can use the sealing array, and manga!Envy would have no way to get any parts of anime!Envy's former body to weaken him. Though I get the feeling manga!Envy's a little more intelligent than the anime version, but maybe that's just me.
I can't even conceive of how the two Hohens would work out -_-.
There would probably be loads of confusion, from the military and Elrics alike until they figured out what was happening with the two Eds. Making their personalities sufficiently different (and yet the same) would be tough. They're not really the same character, but I can't always put my finger on the differences. For example, I always get the feeling that anime!Ed copes with everything that happens to him less well than manga!Ed does. On the other hand, sometimes I think he's got his head screwed on better than manga!Ed.
Would anime!Ed immediately try to go back to his Amestris? Probably not, since he'd feel guilty about inflicting another Envy on poor, innocent *coughcough* manga!Amestris. It would be interesting to see manga!Ed and anime!Ed's interaction. One thing you can be sure, they wouldn't call the other one short ^_^.
Thinking about this is making my head spin, but it definitely is an interesting (read: weird) concept.
Idea bouncing, anyone?