It has been suggested that a form of covenants could be possible using the proposed ANYPREVOUT sighash described in BIP-118.

I’ve created a brief presentation of how I think it would work, and begun to create some simple tests using AJ Town’s anyprevout branch of Bitcon to see if this might work.

I’d love to get feedback from the covenant / vault experts out there. Is this covenant scheme useful? How does it compare to existing covenant proposals like the CHECKTEMPLATEVERIFY BIP-119?

Kanzure’s 2019 mailing list post describes vaults that do not require, but would benefit from, SIGHASH_NOINPUT. The Revault team describes describes a similar scheme. To investigate the use of covenants with APO I built a vault system loosly based on the Kanzure/Revault vaults, but using the current APO branch from AJ Towns to implement them with covenants.

You can read more about covenants in the paper, Bitcoin Covenants: Three Ways to Control the Future.