Migration helper
It is very hard to get questions from small SO tags migrated to suitable target sites. Take for example the latex tag on SO. Every now and then a high quality question gets asked, which would surely get a good answer on tex.se. However voting to migrate very rarely works because there are not a lot of users who will review this tag and most votes will simply age away.
A migration helper could be a user with experience in both the tag and the target site (criteria for example gold badge in the tag and trusted user privilege on the target site) and their vote to migrate would either single-handedly migrate the question or at least reduce the number of necessary votes.