My own employer doesn’t make ABI stability promises for that code, and thus is fine with changing the value anytime it feels like. That’s not a generically viable strategy for a value provided by the standard library.
Additionally, before I sent that email, I looked at a number of the uses, and it appeared as though a great many could be easily modified to use a runtime-determined alignment.
That would be useful feedback on the paper… prior to it getting into C++17. The committee’s POV voting the paper in was that having a constexpr value was something we wanted, and so that’s what we have. At this point in time I’d like to focus on implementing C++17 as it is, and / or filing DRs as required.