As with several other people here, I've had some experience with the Haskell Platform, and have some reservations about a set of "blessed" packages becoming de-facto standard packages, and think that a certain amount of that is reflected in the current state of the Haskell Platform -
Note: as of 8.0.1 there are two download options available — minimal and full. The minimal option is currently the generally recommended one. It does not include any additional global libraries beyond those packaged with ghc, though it does include all tools. This ensures maximal compatibility with a variety of library sets. The full option is useful for those who prefer the "classic" platform behavior with a broader set of preinstalled libraries, and especially serves those well who want full-featured installers in situations where network connectivity should not be taken for granted.
Having said that, I like the idea of meta-packages - I could see myself constructing a personal meta-package over time, with experience of crates that I'd used myself, almost as a reminder of what crate's I've had good results from. And a significant part of the Haskell Platform's problems came with conflicting versions... Would meta-packages constrain the versions of crates that were used, or would that be left up to Cargo? As you said - the devil's in the detail...