The 'an appropriate commit bit access' phrase reads a bit odd to me. Perhaps either 'an appropriate commit bit' or 'appropriate commit access'?

I'm not sure about this detail... There are times that I include non-committers on the review list because I know they are domain experts for something or another. This happens more with ports than with src since most domain experts are already src committers. I suspect this will cause heart-ache when we post it to developers. Also, I wouldn't think of committing a non-trivial vm fix w/o running it by alc, kib, jeffr, etc and having at least one of them sign off on it. I would accept the review from others, but I wouldn't consider even jhb's 'approval' of a phab review to be enough to commit it, even though he has appropriate commit access.

I'm at a lost, though, for how to cast this into words we can use here.

We could say "an appropriate subject-matter expert (usually a committer)." which would let use handle things like numerics where the de facto maintainer resigned his commit bit. I might also add something like:

Some areas of the tree have more strict review requirements, e.g areas documented in the MAINTAINERS file of the source tree or ports infrastructure in the Mk subdirectory.

Maybe tweak this as:

"Note that while anyone is welcome to review and give feedback on a patch,
only an appropriate subject matter expert can approve a change."

s/an/a/

I would be less hesitant and say "is sufficient" vs "may suffice".

Perhaps either "another mechanism" or "other mechanisms"? I probably have a slight preference for the first.

Missing word, maybe "is sufficient when" instead of "is when"?

s/Phabrictor/Phabricator/