Good questions, Mike!! I fall into the category you speak of. I am part of the informal group you speak of, have a modest investment in DCS and Proto 2 and Proto 3 engines, and am concerned about the future. About 3 years ago, I bought a TMCC base and controller from gunrunnerjohn that he had repaired, and have two Legacy engines I have run with it. I bought the MTH cable to connect the two systems, but have never gotten a Lionel engine to run in TMCC mode on the DCS. That scenario may be impractical in the future depending on what parts of the business Mike sells to who. I have run each manufacturer's engine from their own controller with some quirky reactions of the Proto 2 engine when the Legacy engine was on the same track. That was a scenario I hadn't planned on and don't plan on doing on my little layout. I was just testing out a new to me, used Proto 2 engine and forgot the Legacy had power too. I am thinking if any of my MTH engines go South, I'll have to put in ERR boards to run them on TMCC. Yes, I will probably be buying a Legacy system sometime.
No answers, just a commentary on why I appreciate your post.