[joshuamorton]

About half of these aren't specific to polyrepos.

changelogs, reproducible builds, code review, signing, grouped components, distributed builds, TDD smoke test, standardized languages, and microservices are all possible (and just as easy) in monorepos.

You no longer need to worry about versioning, which means no manual updates of either your package or updating dependency versions. Although access control is more difficult, that doesn't seem like a good enough reason to make this kind of decision.