So, it seems you're trying to make the roster bigger! That would be amazing if the team choses the right characters! 
And about the sprites, I, like others who posted before, think thet thay're overdetailed. They looks great, but still... Oh, and yeah, Yoshi looks out of style because everything you've already said.
I'm really looking forward to see this finished! I have my own SMK revamps, but after seeing yours I think I need to work on them a lot more xD
EDIT- Oh, I forgot to mention, if the team acomplish to give each character an own palette, you should try to paint every kart with a different color. Right now, Bowser, Peach and Yoshi look a little weird with white karts.
And about the sprites, I, like others who posted before, think thet thay're overdetailed. They looks great, but still... Oh, and yeah, Yoshi looks out of style because everything you've already said.
I'm really looking forward to see this finished! I have my own SMK revamps, but after seeing yours I think I need to work on them a lot more xD
EDIT- Oh, I forgot to mention, if the team acomplish to give each character an own palette, you should try to paint every kart with a different color. Right now, Bowser, Peach and Yoshi look a little weird with white karts.