I know that there is a feature request pending to make this a review task. But in the mean time can we get an event or something to go through the pending synonyms and do general tag cleanup?
AFAIK, only moderators can do this at the moment AND Stack Exchange doesn't flag up pending tag synonym requests. I for instance happen to stumble upon outstanding requests when going through the tag synonym list during other cleanup tasks. If something has been pending for a while, just ping the diamonds on chat and one of us will process the outstanding queue.