Retagging process should be streamlined.
We need a better way to propose batch operations on tags than what we have now (single thread on meta...). There should be some mechanism to mark a tag as the one to be merged/renamed or deleted. These marks should be visible on tags page so users with privilege to make batch operations could apply them quickly.
We could even try to leverage voting in the process of marking tags. This way if a tag's mark gets X upvotes it could be acted upon.