Template Haskell for cross compilers (port from GHCJS)
GHCJS supports Template Haskell by running it outside the compiler's process, with a different implementation of the Quasi type class. This can be done for other cross compilers too, if GHC gets an option to serialize Template Haskell requests and pass them to an external process.
Someone started the work on this, but I think he stopped. I still have a document with a step by step plan to build an iOS cross compiler, with pointers to the relevant GHC and GHCJS code.