Correct me if I'm wrong: my understanding of how Cabal currently works is that if containers becomes a meta-package for other packages (say, containers-map and containers-seq), then users of the package would have to explicitly specify containers-map and containers-seq in the .cabal file. Additionally, to provide compatibility with older versions, there would need to be some sort of conditional logic too. This wouldn't be easy to automate, since one also needs to convert the version bound for containers into corresponding version bounds for the subpackages. Hence, I think unless there is a way to make it 100% compatible with downstream splitting the package is probably not a good idea, given that containers is such a fundamental package in the ecosystem. Looking at http://packdeps.haskellers.com/reverse , there are about 3000 packages downstream that depend on it (one of highest among the list).