I myself am *very* happy to have other Debian people (DDs, DMs) git push and dput fixes to any of "my" packages. No need for an MNU or delay or permission: just do it. Zero friction. In the unlikely event you do something I'm uncomfortable with I'll just revert it and discuss.
This has nothing to do with a mono repo. It's a social convention, and can be done with per-package repos. In fact, I believe the salsa.debian.org "debian" group is intended for this, with packages having their packaging repos there treated in roughly the above fashion. That's where I put my own packages, unless they belong in some team group. People interested in this communal maintenance idea should be aware of the Low Threshold NMU list https://wiki.debian.org/LowThresholdNmu which is basically the same idea, and I think may have led to a bit of confusion about what a repo being in salsa.debian.org/debian/ means. --Barak Pearlmutter