Agreed there is evidence for SONAR to be useful for some time to come, but the potential for a problem is pretty real for a platform subject to regular change (updates).
The only major issue IME was the Win10 update that exposed a problem with several SONAR VSTs in Nov 2016. The update for both Win10 and SONAR had been checked out on a sand box PC, but the testing wasn't rigorous enough to catch the differences in configuration with the main DAW workstation. That update wiped the existing restore points forcing a recovery from a backup, which happened to be out of sync with the SONAR update and a couple weeks of productivity were lost to troubleshooting. Yes, I could and should have spent more time automating the backup/recovery process while waiting on a solution (since updated after that debacle) but the possibility remains for some future incompatibility. In this case the impact was on SONAR VSTs which affected hundreds of projects. Sure, I could replace the compromised VST(s), but this would assume a remix on all of the affected projects.
Half of solving a problem is understanding what the issue is. The expertise that existed with the SONAR dev team is no longer available nor is any chance for them to fix it.
PCs do not last forever, so while freezing a configuration and keeping it offline might work for a few years, at some point the hardware -will- be updated and compatibility with a legacy OS is far from guaranteed.
It's a bit ironic but worth noting that a pretty standard reply to many requests for help is "Are you using the LATEST version of the program/driver/OS?"
Still reviewing strategies and workarounds (they do exist). Just a matter of time and money.