Yeah, but I'd bet the Turtles are "investigating dimensional energy disturbances" or something and get shunted to the Stranger Things world before the events of the crossover. Almost all the TMNT crossovers involve dimension travel somehow. Ghostbusters, Usagi Yojimbo, Batman...Power Rangers is a exception, but still, usually. It's possible this is one of the exceptions, I guess. Still, using other dimensions just seems like it should be natural, given both shows histories. I can only imagine this ends with Krang inside a Demogorgon's tummy....one way or another.