I'm here because I'm looking for the feature, I'm pleased to see that it's on its way.
My use-case being that I'm building my project in different environments, and it's not clear to me what my MRSV actually is -- I know it's newer than the one provided today in Debian Stable or by repl.it, because at least one of my dependencies fails to compile, but not how much newer. If my dependencies exposed their MSRV then I should be able to work out whether a shiny dependency is worth the higher MSRV.
Something (slightly off-topic) that I'd find helpful here is a version of cargo-bisect-rustc that works the other way around, to discover the real MSRV.