How should the devs know which communities have an Arbcom that needs to approve the bug? I think any system put in here needs to, by default, not interfere with the devs doing their work. Giving communities more opportunities to raise a flag before implementaion is good. But requiring the devs check with X before every implementation, or any process external to Bugzilla, is bad.
The devs only make these kind of changes if someone asks them to, so if the rule is made that only ArbComs (or crats/admins if there is no ArbCom) can make such requests then the devs don't have to check with anyone, they just have to verify that the person asking really is a member of the project's ArbCom, which isn't that difficult. It's certainly easier than trying to work out if there's a consensus for the change.