Fixing opEquals and opCmp

[Fool via Digitalmars-d]

Is there any interest in fixing opEquals and opCmp in the 
spirit(*) of [1]?

Translating the basic idea into the D world would mean:
  - Drop opEquals
  - Encode the type of comparison in the return type of opCmp
  - Adapt lowering

Why?
  - Simplicity: there is always only one function that needs to be 
implemented;
  - Consistency: implementation at a single place makes it more 
difficult to get it wrong;
  - Expressivity: through the return type implementors can 
unambiguously specify the properties of comparison relations 
(Equivalence, Equality, PartialOrdering, LinearOrdering, etc.) 
and algorithms can more precisely specify their requirements 
(e.g. general sorting requires a weak ordering whereas 
topological sorting requires a preorder, only);

[1] Herb Sutter: Consistent comparison, P0515 R0, 2017-02-05
     URL 
http://open-std.org/JTC1/SC22/WG21/docs/papers/2017/p0515r0.pdf

(*) Some aspects of the proposal are unsound but those can be 
easily fixed.