It seems quite clear that the current TMCC system will eventually be going away. For everyone. That doesn't mean that they will not have an omni-board that functions for both Bluetooth and Legacy (they do now) and a converter box that allows Bluetooth signaling from a cab-1/cab-2. Or maybe from a DCC handheld too 
.
They also will sell this board to Atlas and 3rd Rail and make a little profit and economies of scale. Although Atlas and 3rd Rail are probably together less than 5% of the O three rail market, I'd guess.
JohnGaltLines who hasn't posted in almost a year had a mockup converter box that he said worked to operate a LionChief loco from a cab-1, so the reverse (controlling TMCC/Legacy from a LionChief or Bluetooth app) is likely possible and not necessarily all that difficult.
Lots of things are no doubt technically possible, and Lionel will do one of them, based upon feasibility, cost and function. That's what Hitchcock is saying as far as I can tell. I'm happy to wait and see. And while I wait,
I'll go out and feed my horses and lubricate the wagon wheels .
