if they are two codebases with two different maintainers, then it would seem that getting the PR merged is equivalent. you still have two different folks review and approve the implementations, each in a different context. and the spec repo PR also needs to get merged so 2-3 distinct sets of eyes (the spec is maintained by the same person as one of the impl codebases in my case so 2 sets of maintainer eyes for 3 PRs in 3 different contexts.)