I think you've done a great job mapping out the landscape and dilemma for mint operators. One recent development which may help clarify the regulatory situation in the longer term is the NUT-22 Blind Authentication Token. This allows a mint operator to restrict use of the mint to authorized people... this allows, for example, a mint to KYC people at the on/off ramps, but keep privacy at the level of in-mint transactions. This would be much like a bank only issuing and redeeming notes to depositors they know, but not knowing the movement of the cash otherwise.