It probably would be better to create a replacement DAW from the ground up adding all of the best parts of SONAR along with modern, modular code to fix all of the issues. In over 45 years, I've literally written over a million lines of code (possibly "millions") and a lot was done to code around legacy code issues. I've found it's much easier (and takes about the same amount of time and effort) to just write it over from scratch using newer methods. Now you can grab an entire set of functionality, pre-coded and tested instead of creating your own - much better!
If done properly, areas would be modular and users could select different aspects as they wish. Don't like the staff notation? Use a different one. Etc.