My main concern is does the DSiWare save data transfer? Because it didn't when it went from DSi to 3DS.
I don't think so, because the DSiWare titles have their saves inside the games themselves, as opposed to on the card or the system. When they get transferred, all that is really happening is they delete your game (and saved) and then put a new copy of the game (with no save) on the other system.
I doubt this changed with 3DS-to-3DS, which is annoying and stupid. I want to move all my DSiWare games to my 3DS, but the fact I'll lose my progress in A Kappa's Trail and Cave Story has me unsure if I want to. Especially with how hard A Kappa's Trail is. The other games I don't care.
Oh, and Photo Dojo, since I would have to pose/get my girlfriend to pose and us do the sounds all over again. And some of the backgrounds I can't get again.