I attended one of the authoring kit seminar's at GenCon and was pretty damn impressed with what they had. Using the authoring kit you can "essentially" re-write the entire program, GUI and all. But since it's a small company (I believe there are what two-three developer's on board full time, right Colen?) I imagine writing the entire data and game rules from scratch take a chunk of time since the majority of their experience is with d20 based systems.
I know it's taken me two years to get anywhere as close as I am with my gamemode and dataset for PCGen, and I'm the only one working on it, and I don't even get involved with the code, just data.