Unfortunately, scammers will start operating mints without relieving their identities of course and do this so well that they will gain enough trust to hold substantial amounts of btc. Then, they will rug pull. There has to be some kind of collateral that the mint locks on-chain, which gets lost/donated if the mint does not allow users to pull their funds. 

 If I have services for 5 years and get rug pulled for 50$, it still worth it. 🤔

I like your idea with the collateral.