Fragmenting Hackage is bad. But on the other hand I don't see why I
should stick with the inconvenient mtl. Open source software is all
about choice, and as long as the mtl fails to provide the same
flexibility and convenience, I won't use it. Combined with the fact
that fixing it would break existing packages, it appears like I won't go
back to the mtl ever.

So tell me how you do when you have to use a package which relies on mtl's transformers?
You re-develop the package?