Proposed resolution:

This wording is relative to N4849.

1. Modify [range.subrange] as indicated:

   […]
   template<class T, class U, class V>
     concept pair-like-convertible-from = // exposition only
       !range<T> && pair-like<T> && constructible_from<T, U, V>;
   
   template<class T>
     concept iterator-sentinel-pair = // exposition only
       !range<T> && pair-like<T> &&
       sentinel_for<tuple_element_t<1, T>, tuple_element_t<0, T>>;
       
   […]
   
   template<iterator-sentinel-pair P>
     subrange(P) -> subrange<tuple_element_t<0, P>, tuple_element_t<1, P>>;
   
   template<iterator-sentinel-pair P>
     subrange(P, make-unsigned-like-t(iter_difference_t<tuple_element_t<0, P>>)) ->
       subrange<uple_element_t<0, P>, tuple_element_t<1, P>, subrange_kind::sized>;
   […]
   

[ 2020-11-09 Approved In November virtual meeting. Status changed: Tentatively Ready → WP. ]

[ 2020-03-11 Issue Prioritization ]

Status set to Tentatively Ready after seven positive votes on the reflector.

Both LWG 3281 "Conversion from pair-like types to subrange is a silent semantic promotion" and LWG 3282 "subrange converting constructor should disallow derived to base conversions" removed subrange's hated implicit conversions from pair-like types. Notably, neither issue removed the two "iterator-sentinel-pair" deduction guides which target the removed constructors nor the exposition-only iterator-sentinel-pair concept itself, all of which are now useless.