In the Airgapped Wallet Community we also have been investigating solutions, in particular as current common practice is is reuse the same xpub for all multisigs, for instance [90081696/48'/0'/0'/2'] xpub6DYLEkDfCdHzh5FHGHDJksQvFqu6kYANa1sfo6fA8n5ZWkSwyCRVVzyq9LY2eNGB6T9BKDeGJp2ZarjRZHd7WB95nSaFEDhFMK6zSV6D49b

We’ve also have been looking into multi round commitment scheme, but wanted to align the UX so that it would work like to musig for users. Discussion on it is scattered, for instance
https://github.com/BlockchainCommons/Airgapped-Wallet-Community/discussions/16#discussioncomment-212013

Nothing got as far as your version though.

So Concept ACK from Blockchain Commons. Less clear on your specifics though. We will review.

Note that we are releasing a descriptor & multisig centric iOS and Android reference wallet soon so solving this correctly and having interoperability with others is very important for our roadmap.

— Christopher Allen