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Sounds plausible, although it's difficult for me to imagine anyone who should be deeply concerned about losing such amounts.

Possible.
But for someone holding a stable coin, 30 Days is a very large period to incentivize and then a 3 days unlocking period as well. I guess may be first interest payment should be after 30 days, but should be reduced to 7 days or more often after that. Else, holding fund for 27-29 days and then if someone needs to extract/move funds, he would be missing on some decent amount, which isn't great for big holders.

You don't actually have to hold for 30 days. You can only get one interest payment every 30 days but if you hold for one day then sell, you still get the interest but you might have to wait for it (and perform some transaction that affects the balance, even if only by 0.001)