Yes, that'd be the obvious thing to do, but I think right now it doesn't (I could be wrong; I haven't looked at the code for ages).

I did at one point try to specialise everything. The results were hilarious...

    var a = cons(cons(cons(cons(empty, 1), 2), 3), 4);

As the left-hand-side of each cons was a slightly different type, it ended up generating four different versions of the cons function!