The complexity that HKT brings to F# is not just conceptual. It needs to exist in the CLR which will bring implementation tradeoffs.

"Cool paper but no thanks" is a saying for when people come to you with an extremely new technique and want you to incorporate it at the language level with very little proofing in the field.

"Profunctor optics" is the a description of how profunctors encode lenses and similar structures. I am aware. I also think that technique can cook in Haskell land for a few more years before non-research projects should uptake it.