Monero

A decentralized stablecoin needs to be fungible.

Haveno underscores how unusable non-fungible cryptocurrencies are in 2024. Maybe it didn't matter 10+ years ago when people didn't care about coin histories, but it does now. Even though Haveno supports XMR <-> other crypto pairings, you shouldn't buy them there because you risk getting coins considered "dirty" by the system, which are effectively worthless unless you can dump them on somebody else via p2p. What happens if you get your dai there, and then when the time comes to change it back, nobody on p2p will take it from you because of the risk. So you go to an instant swap or a CEX, and they freeze all of the dai you deposited, because of something up the chain that you can't see.

On every transaction, Trocador now says "Do not send funds that have been through a mixer to this exchange". Have coins you buy p2p been through a mixer? Quite possibly, and that's all it takes for them to be marked "dirty". Companies like Chainalysis now control the value and usability of all non-fungible crypto.

Trocador has a "taint" checker, but it's not free (up $2.2 per check), you'd have to check every p2p address before buying, you don't get the money back if you can't proceed with the trade, the information can't readily be shared with other people on the same dex, and you're funding the enemy every time you use it. And the controlling companies may deny access to that information to the general public or to dexes at any time.

Being able to use dai with xmr requires that in the future there still exist non-KYC exchanges which pay out "clean" dai and handle Monero. What if in the future they've all been pressured out of existence? As a nuclear option to cut them out of the system, all the non-fungible crypto they handle could be marked tainted simply for having been through a non-KYC exchange.

If dai uses USDC as collateral, it can be attacked by freezing the USDC it holds. Any decentralized stablecoin that uses non-fungible cryptos as collateral can be attacked by marking the crypto the smart contract or controlling DAO holds as "dirty". This is the scalability problem that Rune Christiansen is alluding to in his recent posts. Once there are too many people using it, there are multiple ways to shut down dai even if MakerDAO doesn't cooperate. It can be delisted from CEXes just like Monero.

The only way that an unfreezable stablecoin can function long term is if it's a fungible/privacy coin itself, and if it holds nothing but other fungible/privacy coins as collateral.

The two advantages you have versus something like Terra Luna is that the reserves can be verified to actually exist, via view keys, and that you don't have to worry about paying a yield.

[edit] The Trocador "marked dirty by chainalysis" check ought to produce a receipt page that can be shown to other people. I haven't tried it, so I don't know whether it does. Then, if you're buying non-fungible cryptos on Haveno, you should put in your terms of trade that the other party is responsible for putting all the crypo they want to trade on one address, checking it, providing a receipt page link, and not adding any more to that address before the trade goes through. Potentially, that way they can sell a lot of crypto to multiple people for only one $2.20 check... if the service remains available.