[stcredzero]

The problem is that the number of possible combinations of versions grows rapidly as you add versions.

The point is not to let people hang out in whatever obscure snowflake version-set they want to. The point is to make migration going forward as painless as possible. However, that expectation is not so much about the tooling as it is about the developer/language community.

To avoid that, you need to standardize on a blessed set of versions to be tested together, much like assembling a release of a Linux distro.

Yes, there should be this! However, you will still have some stragglers and outliers -- this is what the historical reality shows us. The point of such tooling is precisely to minimize the pool of stragglers, not to maximize them!