> The biggest evidence against collaborative editing working and being useful is that programmers don't use it. We go through the pain of having git branches and manual merges.

Hmm -- this seems a bit apples and oranges to me: collaborative editing is sync; git branches, PRs, etc. are all async. This is by design! You want someone's eyes on a merge, that's the whole rationale behind PRs. Collab editing tries to make merges invisible.

Totally different use case, no?