Ecash mint without an every-growing database of spent tokens but a comparatively tiny accumulator. Sounds cool but tmk, a perfect accumulator hasn't been found yet.

If the accumulator has a false-positive rate like a bloom filter, it would falsely flag unspent ecash as "already spent" effectively randomly buring some few of the user's tokens (you can control how little).

It can be improved if the mint shares this accumulator publicly. When wallets want to mint tokens, they could "mine" for secrets that don't trigger a false positive hit with the accumulator. It's still not perfect because the accumulator is likely to change between the mint event and the spend (melt) event - which can again lead to new false positives.