Alright, here's a drawing that sums up all the current Nitro-Fueled character wishes (prior to June 11, of course).
Although Mega-Mix would be a huge stretch. *badum-psh*
Okay, so on July 3 it'll start with the Nitro Tour Grand Prix with the Nitro Squad, consisting of Tawna, Isabella, Ami, Liz and Megumi. No idea when the other two DLC packs come, but the second, Back N. Time Grand Prix has Baby T, Baby Crash and Baby Coco, and that will be followed by the Spyro Grand Prix (AKA Spyro and Friends), whose amount of characters is unknown. That being said…
https://gamerant.com/crash-team-racing-nitro-fueled-spyro/
I love the implication that there's even more coming after those, according to the article writer.