I said it more than once but I think this is a red herring. The pain point is a lack of upstream integrated and mandated runtime type representation.
Even without a built-in deriving mecanism that would improve the eco-system by orders of magnitude, allowing users to define a single value M.repr for their M.t types which can then be used generically by a diversity of libraries of typed indexed combinators (formatters, comparison, equality, ui editors, random value generators, codecs with your pet serialization format, etc.).