I think cashu can scale, but in a certain roundabout way, thought I'm not sure it's possible

If the proof of reserves mechanism that rolls every month for mints rolls everyday instead, then a person could make a system where the normal user would be able to put money on the mints instantaneously but wouldn't be able to withdraw it within 36 hours.

If the issuer of the mint wants to scam people, He/she couldn't do it immediately (he/she would need 36 hours for those tokens to be valid and, by the end of the day, their scam would be detected immediately)

This would preserve the long-time funds of those who put their faith in the mint (because they could withdraw them easily to lightning or other mints) but they would lose their recently acquired tokens

Sounds fair to me and pretty much scalable