So reinventing the wheel, should we do? I am pretty much sure that many have those unity xbox thing. They can give those thing to crackers and crackers can do the rest of the job. Do you not know, sony's phyre engine got it leaked with official sdk. You can even find that on torrent right now. Every time a console got itself hacked, somebody create toolchain/library/simple engine which does not get very far. Because it is huge work we are talking about. I want some really good quality home made games which shines the platform. Unity can achieve this. I mean what more can we ask from one or two people? engine development+game development+art development, its huge task. Unity xbox could lessen the shear amount of work.
Other than post a request here (actually don't, X360 is still current-gen and it's against forum rules) and maybe in other forums, you just have to wait and hope for the best. There's still older dev software for older consoles that hasn't surfaced, but I/we keep our hope up that someday someone will find it and / or share it. You can also try contacting privately people that collect dev software for this particular console and see if you have any luck; just make sure that: a) you are nice to them and ask politely b) avoid sending multiple requests (ie. be patient) c) abide by their rules (if someone shares something with you and asks you to keep it private, do so)