I'm just a hobbyist and have used everything from Pro Audio to X3, but I made more music and had more fun with Project 5 than any of them. It was just simpler to throw something together and then decide whether to put more effort into it or do something else. I have never had the time to figure out how to make SONAR that easy if it's even possible. I bought Live in hopes of using it like that, but haven't had the time to get up to speed on that either.
To steal a few ideas from this thread, here's an idea. Resurrect P5 (exact same UI) with touch implementation targeted at tablet devices like Surface. I'm a developer, and I can tell you that UI design is a huge component of development and it's really done here. Porting the GUI to use x64 and using SONAR's audio engine really seems doable. I agree that P5 was a bit before it's time. I really think there's a market for it.
My 12 year-old son loves loop-based music and I want to help him learn how to create some. I don't even know where to start with him except maybe getting P5 running again or getting something like Maschine. I haven't tried matrix yet. Suggestions?
Re putting the feature in SONAR, I'm not sure that makes sense. Most P5 users don't need much of SONAR, so why add complexity and cost. Of course, making it integrate with SONAR would be a huge plus. Start a project in P5 and move it to SONAR if you want to do more with it.
jpr