+1 for that as a test. A set of test sites with the most popular (free and paid) addons & themes needs to be maintained and tested against every core upgrade. It would also be a good test of @frz’s new containerized quick spin-up hosting package, so serving multiple purposes.
(I expect some of the free addons/themes with most downloads would be buggy even on v8.5.6)
It doesn’t take an experienced developer to do such a test. Developer experience is only needed to analyze when the test fails.