Unfortunately with source code, whilst something may not look that big a job visibily, it can quite a massive undertaking to expose and support points that plug into a UI (I sort of covered that in the last post).. Take VSTs for example, there isn't a week that goes by where there isn't some issue going on. Supporting VSTs I suspect is extremely time consuming, esp when a lot of the time you are helping third party developers fix their issues who don't even pay you for it in return.
From what I see (correct me if I'm wrong) Panu needs Cake to undertake significant work in order for this.... Kickstarter (if you like) to happen. And then they would be expected to support it. If you think this is quick and easy to do think again. I don't see where the revenue comes in for Cake here, and I see it as too much trouble for Cake.
I prefer Paulo's last point as it is realistic as Sonar is not going open source any time soon (except with mackie controllers which (like vst's) can be plugged in).
Anyway I do understand what some people would like to happen, I just don't see it as realistic, even with donations which I suspect would be trivial in comparison to the work. Improving their own UI would be far cheaper and easier.