Mark,
As far as I'm concerned, an "ATC Chatter for Xbox" would not have to interact with MSFS. I'd just want Chatter to play while MSFS is running at the same time. Reason: the phrases used by MSFS's ATC are not realistic (to a pilot in the U.S.). But even worse, on long "flights," MSFS's ATC quits altogether; it just goes silent, without warning or explanation. MSFS users have been complaining about this online for two years, but ASOBO and Microsoft have not even acknowledged the problem let alone fixed it. MSFS's visuals are spectacular, but dead radio silence is not only unrealistic, it's boring. I just downloaded the trial version of FS-ATC-Chatter and installed it on a Windows notebook computer -- one not powerful enough to run MSFS itself, so MSFS is not installed on it. Even without MSFS on the notebook, FS-ATC-Chatter ran perfectly -- so perfectly that I bought the full version of FS-ACT-Chatter, and it runs perfectly too. Of course, because there's no sim radio for Chatter to connect with, I have to manually select the phase of flight I want to listen to. So now, I'm using my Xbox to run MSFS and my notebook computer to run Chatter, at the same time. I have enough room on my desk for my Xbox and notebook computer, but I bought an Xbox because it's portable and I can take it elsewhere to attach it to a large screen TV. I'd be happy as a clam if I could buy a version of Chatter that runs on my Xbox at the same time that it's running MSFS, even if the two were not linked in any way. The only thing that prevents me from doing that is that Xbox is a closed universe; the only software that can be installed on it must be purchased and downloaded from the Xbox Marketplace. MSFS's ATC is so unsatisfying, I'm sure I wouldn't be your only customer.
Lon