What's with all the 80's Turtles lately? I can see the nostalgia bait working in Shredder's Revenge (a love letter to the original TMNT beat em ups specfically targeted to Turtles fans) and NASB (a platform fighter crossover, which always get a good load of attention regardless of topic), but the people who grew up watching TMNT back in the day are by average in their 40's. I don't think they're going to be picking up a Nickelodeon kart racing game if TMNT was the only selling point to them.
My guess is they're just using a softened up, modernized version of the 80's designs as generic catch all designs for the Ninja Turtles, the same way SEGA basically created a new design for "Classic Sonic" to slap onto everything. The actual 80's TMNT don't even really look like they do in all the vector art. They aren't that bright green and their faces aren't that flat.
I think besides Jojo Siwa, the original roster is mostly safe (no, they are not going to remove Lincoln). Crazy to see Jenny's NASB demand now bringing her into all these other games.