Suggested resolution:

Change in 8.7 [stmt.expand] bullet 5.3 as follows:

... The keyword constexpr is present in the the declaration of range and the structured-binding-declaration of u0, u1, ..., uN-1 if and only if constexpr is one of the decl-specifier s of the decl-specifier-seq of the for-range-declaration.

(From submission #908.)

After adopting issue 3048, it is unclear when the constexpr keyword in the expansion should be present.