Have a look at revision 6 of this question. How about adding "flag" buttons for individual revisions? Or should I just flag the question itself, category "other", and specify the revision in the text? (That's what I ended up doing.)
There's really no reason you should ever need to flag a specific revision. It's very unlikely you'd get a user with full editing privileges vandalizing posts in a way that would need flagged. If that were to ever (hypothetically) happen, the proper way to deal with it would be flagging the post and using the other option to explain the situation.
Suggested edits should be rejected before they even make it to an actual revision. If those are slipping through, that's the fault of the reviewers. A revision that actually vandalizes a post is very unlikely to make it through the review process.
The only time post vandalism ever really becomes a problem is with new users who don't know the system and attempt to withdraw their questions, mark them as solved, or whatever other thing they try to do to their question that may be inappropriate. The proper thing to do here is to roll the edit back and possibly even comment explaining to them that this is not the appropriate behavior. Honestly, flagging for a moderator would just get you a declined flag, because there's nothing for a moderator to even do when they get there that you couldn't just do yourself.
If the OP engages in a rollback war and continues vandalizing their post, an automatic flag is generated to attract moderators who will then likely lock it to prevent further editing or flat-out delete the post if it's not worth the effort to salvage.
In a case where someone actually has made an improper edit, intentionally or not, we already have the option to do a rollback.