If you wanted to remake Treasury, here's what i'd do:
Treasury, $4, Treasure - Duration
Worth 1$ each turn this is in play.
(Only discard this from play at the end of your turn if you bought a Victory card).
I don't know Donald's opinion on this, but given the name and how similarly it behaves, i am pretty sure this is the basic concept of Treasury anyhow (at least i was sure enough to state it whenever the topic of Duration-Treasures appeared). But hey, i was also sure Altar was a pun on alter, and i've been dead wrong with that one.
This seems quite overpowered. I mean, it's better than Treasury in almost every way, plus it costs $4 instead of $5. The only way in which Treasury is strong is that the turn you play this, you get 1 less card.
Also, the wording is very awkward. First off, saying that it is "worth $1 each turn", while not too hard to figure out what the intent is, doesn't really work in Dominion rules. It doesn't matter what a Treasure is worth unless you play that Treasure. It needs to give you $1 to spend each turn. And then it needs to specify when you get that (at the start of your turn, at the start of your buy phase, etc). Because of Black Market and Storyteller. And then the discard condition is wonky. A parenthetical phrase is usually a reminder or an additional piece of information about something you need to do; not the main instruction of how the card should be discarded. There's no reason for it to be a Duration at all if it's just going to state on it that it doesn't get discarded as normal.
Meh. Things work in Dominion rules if you say they do. Duration-Attacks were out of the question, suddenly they are there. There wasn't "paying" coins in your action phase, suddenly there is.
I have to dig out the old thread where i suggested Swamp Hag and post the reactions when i have some time. Edit: Obviously i never posted the basic concept here, just the second version that used Embargo Tokens to avoid rules issues.
Also, how is it stronger than Treasury? Because it isn't vulnerable to attacks, maybe? I admit the price was an afterthought (because it doesn't draw cards), but i don't see how a replacement has to deal with "strictly better", at all. And by the way, i definitely think real Treasury is the better designed card, so i'm not really intending to find a replacement. I guess i kind of said that, though. Oops.
I'm mostly curious whether Donald would have done Treasury differently if he had known he would do the things with Durations he is doing today. Because i feel the old Seaside cards managed to do a lot of interesting stuff while still being incredibly simple. Treasury has been a specifically good excample of this.