Modest GHC Proposals
There are many many proposals to augment GHC (and Haskell) that would be valuable yet languish because they have not be documented / collected anywhere aside from persisting in the Mailing lists.
Such proposals are things, typically, that would be uncontroversial and welcomed, but which no core GHC developers have free cycles to work on.
Proposals are suitable for this page if they do not require deep changes to GHC, though they may still be nontrivial, and which ghc-hq is likely to merge in when there is a strong community consensus and well-written patch is on hand.
Many but not all of these may be associated with feature request tickets on the ghc trac: http://hackage.haskell.org/trac/ghc/query?status=new&status=assigned&status=reopened&type=feature+request&order=priority
Many tickets tracked by SPJ also fall in this category: http://hackage.haskell.org/trac/ghc/wiki/Status/SLPJ-Tickets
Expanded Deprecated Pragma
The current pragma can attach to modules or top level entities including functions, classes, and types.
It cannot attach to exports (i.e. if we wish to not deprecate "foo" but only its reexport from module Bar).
It also cannot attach to methods within classes.
There are other possible things we may wish to deprecate as well. Expanding this pragma would make certain changes to libraries more tractable and easily managed.
Perhaps there is a framework to be designed for the following ad-hoc warnings as well: http://hackage.haskell.org/trac/ghc/ticket/8004
Records and Modules
Yitzchak Gale's nested modules proposal which would address one of the larger warts with the current module system and records while adding essentially no complexity to the GHC internals. (i.e. no changes would be needed to GHC beyond the parsing phase possibly, so an easy change to experiment with )
Qualified Module Exports
Delailed here: QualifiedModuleExport
better Adhoc Monomorphization / Specialization support
Currently many libraries achieve monomorphization of code by aggressive inlining. This would be better achieved (with better compilation time) by allowing adding monomorphic variants to stand alone functions. Currently we can only specialize type class instances! Theres also been the idea of supporting monomorphization of polymorphic data types kicked around a few times, but thats a bit more subtle.