Quoted from dendoc:
Great code is only developed once the game is out there and being played. The suggestions made by Pinsiders and tournament players is often implemented by Keith to great effect, so when he says it's 60% complete, it probably means there is tons of room for additions which is a good thing.
Good point. The code on WOZ improved significantly as the game was already sold and on site. TH looks like it already is more developed and, in conjunction with the design changes will be a fantastic machine. There undoubtedly will be future updates the TH code which should help it only get better and better.