It's an interesting idea. Steve Woodcock's been working on the code in acs-subsite to instantiate or create packages, which depends on the fact that Oracle has all the information you need about function parameters stuffed into user-accessible tables. PG doesn't (in part because there are no default values, we've just commented them in by convention).
So we're expanding the metadata datamodel so it will hold the necessary attribute information (the package instantiation code creates a call to the package's "new" routine so needs to know which parameters to provide, their order, etc).
How would your idea work with the query dispatcher, though? I guess people could put the call right in the query file but that's a bit odd ...
