Which is also, of course, what killed interchangeable backs for 35mm cameras. Well, that and the increased size and complexity. And, as you say, sensor alignmrent has to be even more precise than film alignment.
The fact that only one manufacturer has ever done it (Leica, with the last R-series reflex) leads one to suspect that it is less feasible than many would like to believe.
Cheers,
R.