[dllthomas]

You could require some other kind of block interleaved between proof-of-work blocks. For instance, imagine you do proof-of-stake as follows: Any account with more than X btc (as of the previous block in the chain) can mint a block by including as the nonce the previous hash value signed with their private key, constraining the rest of the block such that the only thing to vary in the new block is the time value, adding a rule that between two chains with equal difficulty the one with the earlier most recent POS block wins, and forbidding acceptance of blocks "from the future".

This would seem to lead to a situation where, after a proof-of-work block is minted, those minting POW blocks relax and those minting POS blocks march things forward for each of their accounts until they find the earliest time that satisfies any of them - at which point they simply wait until that time arrives (for themselves or anyone else playing).