This is orthogonal issue.

You can pick any stack, but you don't have to. There still can be general company wide rules about what is acceptable and what is not. It's just that this is informed and enforced by the actual needs (not being too diverse in the technologies deployed), that can change in time independently from contents of any code repository.

Plus you can still make strategic choices here and there, that don't comply with general rules, and have, say 95% of teams working under stricter limits of what's allowed, and this couple of teams with special needs, where you were free to decide otherwise.

Nonsense. Each team owns it's services, and they know best what works and doesn't work. It makes no sense to claim organizational inertia as a valid reason to prevent you from picking the best tool for the job.

To add to that, microservices allow you to gradually upgrade services without having to be blocked by the idea of having to go through major rewrites. You just peel off a concern, get it up and running, and direct traffic to it. Done.