I think this is a non-cosmetic change that deserves a specific feature test macro, because if it is missing, it can be worked around(*), so it's a candidate for conditional compilation for early adopters.

In case you agree, a proposal for the test macro could be __cpp_nontype_template_argument_auto. Does it sound good?

Thanks for reading,

Jordi Vilar

(*) probably, everything could be worked around somehow, not just this :-)