I believe we currently have the technology to make compact proofs of ownership of a certain amount of btc without revealing which utxos we own. Computationally intensive, sure, but compact and quick to verify, even though thwre are 160M+ utxos.

There's a bit of engineering work, but with this, we could embarrass Coinbase Custody into proving they actually hold the coin they claim to.

nostr:nevent1qqsrnxu0j3rsnzel2mh4y8emrmgmh9xqvqv82fn4h6d92jtfltplfhgpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhsygzxljlrqe027xh8sy2xtyjwfzfrxcll8afxh4hh847psjckhkxwf5psgqqqqqqsa22rpk