SWT issue with current Mono

I was tracking a bug in SWT that resulted in a mistake on the API when passing 
strings to g_list. Some imported native functions where being wrongly 
prototyped so when marshaling was implemented correctly in Mono (latest CVS), 
some bugs arouse.

So with the help of the Mono people I now know the way to solve this in SWT, 
but this got me thinking. Why not use Gtk# to solve the low level stuff like 
importing Gtk functions, converting back and from unicode, and other millons 
of issues? (notice that not even Gtk# tackles the conversion of unicode 
strings correctly yet, but when they do, SWT will have it done right).

I know this creates a dependancy on Gtk# and adds weight to the API, but how 
much it would affect the perfomance? Let's say we do (this is a stupid 
example):

namespace SWT.Widgets {
	class Combo : Gtk.Combo {
		// ...
	}
}

Would this really make the API much slower? You now do all the importing and 
conversion of native to managed data types...but doing this all that will be 
done in the Gtk# binding.

I haven't studied this profoundly, but if it can be done, I think it would be 
the best way to do it and I am interested on helping with it.
What do you think? Do you see it possible?

Pablo