Reggie isn't exactly a game designer, so it's impossible for him to work on Smash Bros 4.
As for Iwata, at the very least the 3DS version will happen. Wii U would as well actually. But I feel there's barely any options above that would apply to how Iwata would handle it. He's pretty reasonable (also he was responsible for doing many cool things as a programmer!). The content would be different for sure though, he can probably pull some miracles that the programmers weren't able to do.
He was responsible for fitting both Johto and Kanto into Pokemon Gold/Silver. The developers had issues having the entirely of Johto being put into the game, so he helped compressed data and it had enough space for an extra region, so thus Kanto was added! He also ported the R/B battle system into Pokemon Stadium 1 without reference codes or documents! The man's crazy awesome with his programming! He even saved Earthbound from development hell!