The in_place constructor that takes an initializer_list has both a Requires: for is_constructible and a Remarks: for is_constructible. The one that takes just a pack has just a Requires: for is_constructible.

I think both of those should be Remarks:, i.e. SFINAEable constraints. Otherwise querying is_constructible for an any with in_place_t will not give a reasonable answer, and I utterly fail to see any implementation burden in SFINAEing those constructors.