aut-ct already works as a tool, and can do this. I just need some people to pay attention to it, as well as audit it. But I'm not particularly optimistic about that.

With most such tools it's often better to just "launch" something as people's usage will attract the necessary attention. For a "this proves I own bitcoin in this range across N utxos" tool, as exists in aut-ct, the natural user is some medium size bitcoin business that wants to prove utxos with privacy, a much smaller group, more conservative in its actions (and indeed, I can't even recommend using it without some audit, anyway).