If google were nefarious, they can secretly ship a new version that supports both versions of the protocol, wait weeks, months, or even years for it to become installed almost everywhere, and then silently remove support for the old version from their servers.

That would give microG zero time to prevent their software from working uninterrupted.

That sort of thing can happen for all sorts of legitimate reasons, it's not necessarily nefarious. For instance if the client side of the project is running ahead of the server side, rollout may begin with usage controlled by server-side variables. Once the servers are ready to go, usage may be ramped up much faster than software rollouts themselves happen.

Also IIRC the Google services are updated automatically in the background anyway by the Play Store app. So I guess rollouts can happen quite quick regardless.