Currently there's two ways "approval" can be determined. 1) Approval by "any" of the reviewers means it has passed. Ex. The 3 people with write-access get chosen as the reviewers, and if any 1 of those 3 approve it, then it passes. 2) Approval by "all" of the reviewers means it has passed. Ex. Of the 3 people chose as reviewers, all 3 would have to approve the PR for it to pass.

Does that make sense? I think #1 gets at the scenario that you're talking about, but right now it doesn't automatically choose the reviewers based on who has read/write/admin access. You would just choose those people manually when you set up the repo and choose whether the rule is "anyone" can approve it or "everyone" has to approve it.