Berin, i'm working along the same lines, of having a serial controlled pic control seperate stepper boards. That way it can be used with the open source board designs or like you say gecko boards. To have the pic output step/dir would be more of a programming matter then hardware would it not. Picstep is a cool idea but it is only using the chips to work on each board but is still driven by lpt port.
If you haven't seen luberth's site.
http://cstep.luberth.com/