Obviously I can't speak for MassDrop, but as a rule they are very open to small projects, even ones where only 150 units will be sold. They really like collaborating with community designers on fun, unique projects. Rocketeer is one such example. So I would encourage anyone with an interesting idea to reach out to Yanbo at MassDrop and see what he has to say, even if it is a fairly small scale project.
Now matt3o may not have the official authority to veto a keycap set that proposes to use MT3, but he can certainly play the role of facilitator since right now he has more influence with regard to his new keycap family than anyone else outside of MassDrop. I don't know the details of his business arrangement with MassDrop, but I would venture to guess he has some degree of controlling interest, so to speak, over the MT3 family.
As for Rocketeer, the project was only ever going to be a MassDrop thing. There are too many other elements to pull together for anyone else to do it and do it the way I would want it done (and with the broad reach MassDrop has). Remember, Rocketeer isn't just a keycap set.