I think it would be useful to be able to test whether the lower version bounds for the dependencies of an opam package are actually correct and compile without errors. There seem to be a lot of PRs in opam-repository that are basically “bump the version requirements for X package”, so maybe it could be added as an explicit check before merging a PR.
From what I understand, it should be possible to pass some preferences to the opam solver that make it select the lowest possible version of all packages to install, given a set of dependencies (similar to the “minimal version selection” in the vgo proposal), but I’m lost on the preference language.