The reason I went straight to using a custodian is that the collaborative custody services all feel very very close to custodianship to me.

The primary benefit of a collaborative custodian presumably is that they can't rug you. This is only true if you have control of the quorum of keys.

If you don't have a quorum, then you really really need to do the digiligence on who the third party is (how do you know the third-party keyholders won't collude? how do you know they are even that separate of entities?).

If you do have a quorum, then aren't you just better off keeping a backup key in a safe somewhere or giving it to a trusted friend, family member, lawyer).

I can be convinced the concept is misguided, though. It's more an interest in why self-custody isn't taking off and the somewhat elevated base-level of anxiety I carry with regard to my own efforts at self-custody.