A friend of mine and I are having a discussion and I'd like to see how everyone else thinks (especially any devs that may read this)...
I believe, as most do, that when a Villain or Hero switches sides, they gain access to Paragon City or the Rogue Isles, respectively.
My friend believes that, due to coding issues and what-have-you, Heroes and Villains will instead see a sort of instanced or Praetorian version of their new home rather than the much-hyped ability to legitimately switch sides.
Just a note, the press release and FAQ are all worded vaguely enough for neither of us to have concrete proof.
Any confirmed clarification for this would be much appreciated.
Also, of the small amount of info we've gotten from the devs, they've mentioned repeatedly that they are including a new starting area, and hinted that it'll be a mixed/co-op zone, where Hero and Villain ATs can work together. I think it was also mentioned somewhere that this would likely be a "neutral" zone, in that anyone who starts here would probably be in the grey zone morally. (So if you wanted to run a Mastermind to Atlas as soon as possible, you might need to start here.)