Given you aren't sure since SG1 this might be useless but... do you have a paper number? Or, more likely, know an author's name ?
(is the current version of that paper, the tracking ticket insisted there's a P3125R5 and that LEWG had seen it in 2025, but it isn't listed in a mailing so it might be a mirage)
You know it's a Hana paper because it wants this to be allowed at compile time (C++ constrexpr) but joking aside this seems like a nice approach for C++ which stays agnostic about future implementation details.