I think this will work best together, rather than instead of, hash-based mining. Blocks are confirmed with hashing as normal; this is enough for casual double-spend attempts. When a block is old enough, stakeholders can sign it. If a major attacker tries to build an alternative branch, clients will reject it because it
We already have this in the form of checkpoints in the client software. You don't need voting for it, because there is no ambiguity or controversy about the identity of the block hundreds of steps ago. Better to have a check performed by _everyone_ than just people that happen to have a lot of bitcoin already.