The user also told us the presumably minimal compatible versions of project's dependencies. Why don't we plan to use -Zminimal-versions by default after its hypothetical future stabilization?
The same point applies to some other listed reasons.
And may significantly delay discovery of issues in new dependency versions which have bumped their MSRV above project's MSRV. Even worse, such issues will affect downstream users first, who are less likely to be able to properly diagnose such issues.
The "too-new" API problems which break MSRV of a dependency should be found and resolved directly by dependencies, not by downstream users. Correctness of minimal dependency versions should be separately checked using -Zminimal-version, MSRV-aware resolver is a wrong tool for this problem.
I believe the suggested approach should be developing with the latest stable (or even, in come cases, Nigthly) toolchain and check MSRV as part of CI, ideally, together with minimal dependency versions.