I have mixed feelings whether I want to see them stand alone or together with a trainer. Obviously I'd want stamina crap gone and all the other hinderances.
Now regarding this thread. Are they really on their own? Some things I find fishy are:
-They were both introduced in the same video.
-Water and Fire type have been fulfilled leaving Grass to complete the gap.
-Making them an all in one leaves room for Mewtwo and Jigglypuff.
-Sakurai's a troll.
COUNTER ARGUMENTS
-Tranforming characters do not exist.
-Final Smash would be unique to all Pokemon.
I honestly think it's a possibility. There aren't many Grass types that would make a good transition to Smash(usually on all fours, if not, hunched over, tend to be overweight looking, etc.) except one I can think of at the moment. And that's Sceptile. Though, he isn't the most popular starter he definitely can work as a character and looks VERY easy to translate into Smash. I definitely see him as one of my favorite Pokemon so I am a little biased here.
Other than that, Sakurai can be hiding the trainer in the background until he releases the Grass starter. IIRC, that did happen during Brawls PT early video's.