Also, GHC's current plan for the base library:
http://hackage.haskell.org/trac/ghc/wiki/DarcsConversion#Planforlibraries
essentially means forking base (as nhc98 would continue to use base in a
darcs repo, while GHC would use it from a git repo, and there are no
plans for any merging between these repos). Therefore any code that is
to be shared between the implementations needs to not be in base, so
from that point of view it would be good to pull out as much as
possible.

First the easy bit: The Data.Generics hierarchy is going to have a
separate maintainer, and I think that everyone is agreed that it should
be pulled out into an "syb package". I'll treat this as not part of base
from here on.