Oh god please no. I want to be using Gitlab 5 years from now, not planning a migration back to Github or whatever when Google loses interest in another toy.
If Google acquired GitLab, they'd offer it as a managed platform for GCP, which they're unlikely to shut down since contracts and SLA require a heads up of about a year before they can remove a service that is GA from their platform.
Just look at Google+: it still lives on for G-Suite customers while the public version has been shut down.
I don't expect GitLab to be of much interest to Google though: A lot of their stuff competes with services Google has on GCP, Ruby/Rails doesn't fit that well into their Python/Golang/Java stack and a remote-only company wouldn't fit into their office-bound culture.
The whole reason I picked Gitlab is that it doesn't matter what Gitlab does, if they pick a weird direction I can just self host and do what I want.
Gitlab is big enough that should they ever be killed by a Google acquisition (I don't think that's likely), a strong enough community would sprout and keep maintaining it.
Do you have examples of open source software in a similar situation (one company providing coordination and final approval in the previous project; similar complexity level to Gitlab, whatever that is), where that happened successfully?
I'm not challenging necessarily, I legitimately am interested in examples.
Hmm what about the Blender project, would that one count?
I admit it's difficult to come up with examples, though I don't know of any failures either. RethinkDB has been sort of a failure, but it was never very popular to begin with.
You can't compare that as it's a paid enterprise on-prem version not something you can self-host and keep running as long as you want. You won't get community fixes for it like it would be the case if Google were to abandon Gitlab if an acquisition would be the case.
