Very nice! Why not include a new body, which would be the cheapest part!. Not sure that it'll tempt out of the 502X though. Open belts on dusty tracks?? The new Losi 22-4 has an enclosed system for similar spec. So the 503 will need to be keenly priced and well supported.
Mmmmm....the 201XM and Egress 2013 have left some big dents in the racing budget of late!
Additional: a close look at the Parts tree shows (bottom third of image) nice blue 12mm hex's near the new universal joints:
http://tamiyablog.com/wp-content/upl...g_2014-163.jpg