Semi-applied datatypes in instance declarations

[George Russell]

I apologise if this has been raised before, but the code I am
writing now would look rather nicer if "partially applied 
type constructors" were permitted in instances.  For example:

class Event e where
   sync :: e a -> IO a

data Event extraData a = blah blah . . .

instance (context on extradata) => Event extradata where
   blah blah . . .

Any chance of this?  Or are there reasons why this would be wholly
ridiculous?