I personally don't see having the version in the package address particularly more nasty than specifying it in the project file, as in Maven, which I have been dealing with lately. One problem I imagine is that when migrating to a new version of a library, the address has to be updated in each file the library is used in, with potentially catastrophic consequences if any one file is forgotten. A grep seems wise in that case.

Would you argue that there are more robust solutions in the Haskell ecosystem? What scheme do you prefer?