If Zelda and Mario lose a character, I won't be surprised if the Pokemon cast would also stay completely the same. I think it's likely that Mario and Zelda at least get a new character, only for the fact they didn't get one in Brawl. Especially Mario. Really, really wanna see Toad make it. Impa as well.
They make sence, as they're both kinda like the protectors of their princesses. I don't think any other franchises besides Mario and Zelda would have the right to have supporting characters as them in Smash. If Impa is separate from Zelda, we'd still have 5 Zelda characters on the roster. And with Toad's inclusion, Mario and Zelda are even again, like in Melee.
Overall I want the Mario and Zelda franchises with 5 characters, so that any other franchise can get more characters to compensate for that. Like Donkey Kong, which wouldn't then be so bad having 4 DKC characters next to 5 Mario characters for example. If they leave Mario at 4, even King K.Rool would be hard pressed perhaps...
Diddy also wasn't even a semi-Mario rep...
Heavy weights need more poking like attacks, to keep the faster characters at bay. Donkey Kong can semi-effectively do this sometimes due to his long range, but he suffers from predictablity, as the only move on par with most fast characters is his very predictable Back Aerial. Still, loved the hell out of Brawl's DK though!