IIRC, Bitshares was looking into adding "custom keys": keys which allowed for a given subset of operations to be signed. If it's not too intensive, this could be a useful feature for Hive as well. For example, a user could create a key that could only be used for voting, but not for posting, preventing potential identity theft when providing a voting key to another user or service.

Maybe someone from BitShares can chime in on if this was implemented, and if so, how easily/usefully it might be implemented for Hive.