[Haskell-cafe] Arguments against an hypothetical Data.ByteString.Generic?

Hello, As vector provides a class generalizing all flavours (Data.Vector.Generic.Vector), it occurs to me that the same could be done for ByteString. Then, packages based on it would have the choice between hardcoded and generic, they wouldn't have to duplicate a module to handle both strict and lazy versions, as (with the exception of functions for communication with C code) they already provide the same API. I would be willing to make it, it's a concern I've had in mind for a long time, but as I'm pretty sure the idea isn't new, I would very much like to know if and what arguments (related to performance maybe ? I don't know...) were raised against that.