1. According to things that Hoenheim said, the dead of the FMA-world go to the AU-London world (for lack of a better name; I mean, it's NOT our world, London here was never actually invaded), right? And Hoenheim and Ed ended up in their own bodies at the end of 51 due to being shoved through the gate (or Hoenheim ended up in one so similar that his wasting disease affected it as well), correct? Therefore I assume that I assume that the FMA-world dead get their bodies through something akin to reincarnation, or else you'd have newly-inhabited people running around going "WTF?" all over that world and demanding answers as to why Heaven looked less than up to snuff.
2. Sooooo... you have to wonder if Ed'll run into people he knows there. Granted, it'd have to be in a few years so that they get past infancy; but wouldn't it be interesting for him to meet a child with Hughes' eyes and personality? Or Nina's, or (aaack) Scar's... Or his mother's, for that matter. His mom would be, what, about 7 or so at the time of his crossing over if she reincarnated immediately, wouldn't she? Intriguing thought.
3. Another odd consideration: Do people who die in the FMA-world of alchemically-caused deaths end up transferring directly through into similar bodies in the AU-London world? That'd cover Scar and Nina and any of the alchemists that Scar killed... and all those soldiers who were vaporized to make Al into the Stone, too. Hmm. VERY odd thought.
So, am I just smoking crack here or what?