Since the last related correspondence on this list [0], a number of
improvements have been made to the OP_VAULT draft [1]:

* There is no longer a hard dependence on package relay/ephemeral
  anchors for fee management. When using "authorized recovery," all
  vault-related transactions can be bundled with unrelated inputs and
  outputs, facilitating fee management that is self contained to the
  transaction. Consequently, the contents of this proposal are in theory
  usable today.

* Specific output locations are no longer hardcoded in any of the
  transaction validation algorithms. This means that the proposal is now
  compatible with future changes like SIGHASH_GROUP, and
  transaction shapes for vault operations are more flexible.

---

I've written a BIP that fully describes the proposal here:


https://github.com/jamesob/bips/blob/jamesob-23-02-opvault/bip-vaults.mediawiki

The corresponding PR is here:

  https://github.com/bitcoin/bips/pull/1421

My next steps will be to try for a merge to the inquisition repo.

Thanks to everyone who has participated so far, but especially to AJ and
Greg for all the advice.

James

[0]:
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2023-January/021318.html
[1]: https://github.com/bitcoin/bitcoin/pull/26857