Mxy will never see the light of day in a live action movie....actually since the reboot I dont think where ever going to see him again
Prankster just isn't.....enough....maybe as a side villain like Scarecrow in Batman Begins but as the main baddie no way (same applies to Toyman, only he could be exactly like Scarecrow and come back in future films).
I'd love to see Conduit show up, not as well known as alot of the other villains, but his back story would be awesome and fits well, someone who grew up in Smallville with Clark and is actually going after Clark and not Superman
now that would be a cool twist in the movies