[tlrobinson]

I believe your DPR use-case is possible with Bitcoin, using "lock time" contracts. https://en.bitcoin.it/wiki/Contracts

Every transaction can have a lock time associated with it. This allows the transaction to be pending and replaceable until an agreed-upon future time, specified either as a block index or as a timestamp (the same field is used for both, but values less than 500 million are interpreted as a block index). If a transaction's lock time has been reached, we say it is final.

[gwern]

Yes, the specific case of a fallback is possible, but not the general time-lock case. I think. I was discussing this a little with the Bitcoin developer mentioned there, Mike Hearn, but I quickly got out of my depth and the conversation petered out.