I was just looking into the conventions around this yesterday! It seems like this proposal is mostly just formalizing stuff that is already a tacit standard. I'm glad to see that someone is documenting it somewhere more "official".
It appears consistent with
https://github.com/bitcoin/bips/pull/253, However, due to historical timing, the PR you linked doesn't include any standards around segwit conventions.
In the review thread you had mentioned that you needed an ACK from prusnak, but he explicitly gave a NACK in favor of a separate proposal for BIP 48, which seems like it could be something like the OP. Reading the proposal it seems consistent with the pull request that you linked, as well. At the end of the thread the author of PR#253 said they would open a separate proposal, but it appears that it never materialized. Was there a reason for this?
Keagan