Proposed resolution:

This wording is relative to N5008.

1. Modify [tuple.cnstr] as indicated:

   template<class Alloc>
     constexpr explicit(see below)
       tuple(allocator_arg_t, const Alloc& a);
   […]
   template<class Alloc, tuple-like UTuple>
     constexpr explicit(see below)
       tuple(allocator_arg_t, const Alloc& a, UTuple&&);
   

   -32- Preconditions: `Alloc` meets the Cpp17Allocator requirements ([allocator.requirements.general]).

   -33- Effects: Equivalent to the preceding constructors except that each element is constructed with uses-allocator construction ([allocator.uses.construction]).

   -?- Remarks: These constructors are defined as deleted if is_reference_v<T_i> is `true` for at least one T_i.

Per [allocator.uses.construction]/1, uses-allocator construction is only defined for objects. And presumably, an attempt to construct `std::tuple` of reference from an `allocator_arg_t` constructor causes a hard error.

Since C++23/P2255R2, it seems that these `allocator_arg_t` constructors are conditionally deleted according to [tuple.cnstr]/33. However, it's confusing that these constructors are sometimes non-deleted when the tuple contains a reference, while there are hard errors in an instantiation instead.