I'd also appreciate +1 and -1 votes on the overall idea, in case this entire feature, regardless of implementation, is simply something the community does not want.
-1, at least as part of core. My question would be how much of this is would be needed if someone were to create an external project that installed a "pg" command on top of an existing PostgreSQL installation. Or put differently, how many of the changes to the existing binaries are required versus nice-to-have?