I am also waiting for the XP12 version of the TBM900. And of course, I am also not happy it is taking that long. It is apparently not easy. But maybe also not rewarding enough from a financial perspective.
I feel it is important for all of us simmers that developers have a healthy financial incentive, also for an important update. From that point of view, I never understood why the XP12 version would be free of charge for owners of the XP11 version. Maybe it makes sense for very recent purchases in order to protect a cash flow for the old version while waiting for the updated version. I doubt whether that will work when an upgrade takes many years like in this case. A discount for XP11 version owners may make sense, but free of charge is too generous. I would accept a subscription based model, safeguarding a longer term revenue stream for the developer and incentifying updates.