Also that you're relying on OpenTimestamps. It theoretically scales well, but if it's a vital link in a trust chain people will spam it either for value or for DoSing honest updates. It's simpler to attach PoW to kind:0 updates, that way the attacker bears the cost

Sorry, i dont follow....at all. What do you mean by 'spam it either for value or for DoSing honest updates'. Also its funny to me you talk about PoW because any PoW idea is absolute shit