I might ramble a bit I am so sorry-
I can imagine if all the brothers survived along with Casey Jr. in the future, Donatello starts making tech as everyone rebuilds the city. Soon most tech made by Donnie or with his help protects the city while they live in a futuristic world where humans and mutants walk together
Or after that day of defeating the kraang Donnie can slowly make peace of their mutant appearance, some people still being against mutants but he helps with upgraded tech that'll keep the city safer
If any of this confuses you I'll try to clear it up (my bad if my typing is wonky)








