SegWit had its own BIP for adding fields, but that was a significantly bigger lift. My preference would be to just extend BIP54, as I've done below.Feel free to respond on the list or here: https://github.com/bitcoin/bips/pull/2097BIP54’s consensus fixes are currently uncontroversial.Bundling new getblocktemplate additions into it changes that and expands the policy surface. Those additions should be specified separately, where they belong.