Although I respect your opinions on this, I disagree for a few reasons:
1. The existing Sonar does not have a small footprint. It is a large program that is prepared to do a million things other than playback at any given time. I want something portable. Say a computer goes down during a show. Can you take the jump drive backup of your show and put it on any other computer quickly?
2. There wouldn't be any reason for testing. It could be the same layout as the Sonar you're already familiar with. Just with playback only.
3. This one I do understand, however here's my situation: I am FOH for a tribute band. They want to control the playback on stage, so having this standalone program would be ideal. They want to skip a song? Fine. Some other whatever? Have at it. So they'd be pumping audio via USB into the X32 monitor rack on stage.
That feeds my X32 at FOH, where I can record those tracks PLUS the live performance into Sonar off my desk. So being able to record, for them, is irrelevant. Everyone wins and I don't need to have another full copy of Sonar for them to somehow screw up onstage. So playback only is a total win-win here. And I've worked with several touring bands in the same situation. They only need playback up at the stage. FOH can record there if they want it.
As for the matrix, it might be the answer, but for non-electronic, loop-based music, I don't know if it fits the bill. I can just have the loop on and let it go until they want to be done, have a trigger pad that turns the loop off, and they continue. Simple. If I see that the matrix works for linear tracks, then maybe.