GHC-specific package(s)?

[Ross Paterson]

How about a package (or packages) for modules that support experimental
GHC-only language features, like Generics (currently in base) and
Template Haskell (currently in haskell-src)?  This would make it easier
for other implementations to ignore them (they do tend to move around
a bit) and also present a distinction in the library documentation.
(It might even speed up the GHC build a tad, because you don't need the
rest of haskell-src for stage1.)