I can't imagine that purpley Braixen is Fennekin's final form. Hardly anything changes from Braixen's design... woo purple stuff on her wand and purple ear color.
For the witch concept 4 legs would be just strange and it would make less sense than being Bipedal
None of the evos will suck, not Quilladin sucks. Gen 6 has the third (maybe second) best evos right now
Well, I hope not. Grotle was a mess as well yet it evolved into the iconic Torterra so I'm semi-fine with Quilladin as of now.
I just pray it's not a Meganium-sized mess.