Let me summarize :-)
The current design for type functions with result kinds other than * (e.g. * -> *) has not gotten very far yet. We are currently stabilizing the ordinary * type functions, and writing the story up. When that's done we can properly focus on this issue and consider different design choices.
thanks, seems i was too optimistic, then!-) btw, i noticed that the user guide points to the haskell wiki only, while the latest info seems to be on the ghc wiki. given the number of variations and the scope of development, it would also be helpful if the user guide had at least a one-paragraph executive summary of the state of play, dated to clarify how up-to-date that summary is. that would avoid discussions of not yet stabilized features (should ghc issue a warning when such are used?). claus