Quoting Hawke from http://chatlogs.metabrainz.org/brainzbot/musicbrainz/2015-12-17/?msg=3442669&page=4

[...] I so often come across edits that I can't or shouldn't vote no on but which have some problem which should be resolved after the original edit is applied...

You can use bookmarks to save edits, but if it were in-site, it could be tied in with a notification system. e.g. We could send a notification when an important edit changes status or is commented on, or we could say "You haven't looked at edit #X in Y days," or something similar. I don't think it should be encouraged as a permanent flag, for that people can use bookmarks.