Now this is all speculation and only should be thought of in that way- now, shall we begin.
Back in the day when TMNT was in the comic bizz they shared a key object with another famous hero, Daredevil. Yes the same canister that caused Daredevils blindness also caused the turtles to become crime fighting teens. Now that Disney/Marvel owns the right back to Daredevil could we see our favorite turtles to join with the Avengers, in comics the turtles have been published by Marvel a couple of times and even have teamed up with some of our favorite hero's such as Daredevil, Iron Fist, and Punisher. Now will the turtles team up with Joss Whedon's Avengers probably not, will they ever team up with the maybe, would it full fill our fan boy dreams most likely.
In the comments below tell me if you would like to see the heroes in the half shell team up with earth's mightiest hero's.