Yep that’s another possibility but it’s a much more limited anon set and it’s kind of a different model to the usual taproot one; with taproot the idea is that a utxo has (better, might have) a locking script that you don’t see on chain.
That’s in the category like “anon set of all the users of this protocol”; for that you might want to do things very differently. E.g. "all lightning network nodes that are choosing to engage in this protocol publish a key (somewhere, somehow) and a locking script for their utxo and then all the other members can accept a request to participate that attaches a ring sig or ZKP that proves that they own one of the keys+timelocked scripts that “registered”.
The aut-ct thing is geared around the other extreme of “anon set of all taproot utxo pubkeys that satisfy a public filter” so much larger anon set but much more limited on the conditionality. Hope that makes sense.