> The SHAKEs were low hanging fruits to implement, so I included them.

I don't think this is sufficient motivation.  Each new API is a permanent maintenance and documentation burden.  It is also a burden to every new user seeing the module and trying to decide which offering to use.  We should provide tools that we know people need and error on the side of economy.  I asked a room full of network engineers about SHAKE and not a single one of them had heard of it, so I think it would be premature to add to the standard library.