Of all the stuff mentioned, I think the TF/G.I.Joe crossover might be the most likely to actually happen. Hasbro owns both properties and there's actually established media supporting it (or at least the general idea of TFs and Joes together...I never read those comics, so I'm not privy to the deets). I think the possibilities are pretty interesting. Who knows how far they'd go, though, and what kind(s) of figure(s) they might start with to test the water. My guess is a transforming trouble bubble would look stupid...lol...probably start with a HISS tank or Vamp...Sky Hawk...AWE Striker...something like those.