There are several things that I'm curious to see whether they'll somehow migrate them to to DCA or if they'll be lost because of the change in parks. Among my favorites are the Cadaver Dans, the Frontierland Dragon (formerly the Fantasyland Dragon), the Toontown Pre-Party, and the AP Treat Trail.
I'm guessing the AP treat trail will move (that seems pretty easy and doesn't really require any special space). I'm also hopeful that the Cadaver Dans will make the jump, but I don't know if the Undertaker theme will work as well in DCA (given that there is no Haunted Mansion). Maybe something to tie into Carthay Circle area would be cool. I can't really think of anywhere where the Frontierland/Fantasyland Dragon would fit, but maybe they'll surprise us and it'll still be in the cave by Big Thunder.
For the Toontown Pre-Party, hopefully they'll have something like that. I can really only think of two kind of easily isolated areas. One is the Redwood Challenge Trail and the other is the Hollywood Land side area (by Monsters Inc). The latter isn't very big and it would block off two attractions. Redwood Challenge Trail sounds like the most logical location, but it seems smaller than Toontown and harder to navigate. I suspect this one of those things that we might know about until after the first party starts.