I think they need to get a dialog going with Sonar users and compile a dossier of show stopping bugs, design flaws, annoyances and other workflow killers and frustrations. All the things that make people yell "goddammit" at the screen 100x during every session. Many of these issues are minor but there are so many of them and the accumulative effect can be to make users feel like they're fighting against the program instead of working with it.
There is a ton of this "minor" stuff, like for instance: many times during a session I will accidentally click on the "show automation lanes" button on a track, and despite the fact that I have no intention of automating the volume, Sonar will give me an automation envelope hardwired to the fader simply by virtue of my having clicked that button. I have to manually delete it. It's a "show automation lanes" button, not a "create a volume envelope" button. Big "tch" moment every time I do it. If there are no active automation lanes on the track, just give me a blank lane and I'll choose a parameter for it if I want! I wonder how many times a Sonar beginner has done that, closed the lane and then wondered why the volume fader keeps snapping back to unity every time they try to move it. Stuff like that is horrible design from a user experience standpoint.
Loads of stuff needs polishing up, like the way in which you select parameters for an automation lane. It's all very well and good when you want to automate the pan pot or something which is right there at the top of the menu, but let's say you want to automate an EQ band on an EQ with a dozen possible bands. You end up having to scroll through an endless list of parameters in a menu in which you can't even use your scroll wheel. It's horrible.
Make the mapping of controllers to mix controls and VST controls easier and more intuitive. It frustrates new users and even long time users. Update old and awful parts of the program, like the horribly counter-intuitive and frustrating keyboard shortcut manager. When you compare it to shortcut managers in other DAW's it's an abomination. Update the browser. Make the export dialog less confusing and more in line with how people would expect it to work - this has always been a huge source of confusion among users judging by forum posts ("I exported a track and it sounds nothing like the original" etc).
Have automation nodes show the PROPER value of what you're automating when moving them or hovering over them. When I'm automating a filter cutoff and the node shows "65%" instead of the value in Hz, that's super annoying and so unhelpful.
These are just a drop in the ocean of similar little annoyances and sloppy design which together contribute to the feeling of Sonar being "unpolished." They no doubt drive a lot of people away. Fixing this stuff along with some of the long standing, stupid bugs which should have been fixed years ago should be the #1 priority, and I'm sure BandLab and the new team will realize this.