I think the note is in the right place. From CWG 2140:

The current rules in 4.1 [conv.lval] paragraph 2 do not require fetching the value in memory of an object of type std::nullpt_t in order to produce its prvalue. This choice has implications that may not have been considered for questions like whether use of a std::nullptr_t that is an inactive member of a union results in undefined behavior or whether a volatile std::nullptr_t variable in a discarded-value expression produces a side effect.

The rules are now in paragraph 3, but otherwise this comment still apply.