Veni, Vidi, Converti
Unity is in many ways the opposite of BigWorld from our planning perspective. The client is more advanced and includes a number of tools that aren't included in BigWorld. It crucially already includes a full DirectX 11 renderer, and we can immediately tell the difference in the rendering quality of our Tech Demo environment. And though it does not include an MMO server out of the box, several third-party solutions have been created to fill that void. When we started adding up the numbers, it looked like we'd need about the same level of investment to implement the server side with Unity as we'd planned for updating the renderer of BigWorld.
We have a few other reasons for choosing Unity. We get to ship with a Mac client, which was a very highly requested feature both from our fans and from Paizo. We can even investigate putting some extra features using web browsers or on mobile devices, like the Environment Walkthough we just posted, which lets users with high-end graphics cards walk through the environment we built for the Tech Demo using a web browser. And the overall strategy is a better fit with our existing team's skill set: I have never been a graphics programmer, and we were going to need to hire that expertise. But I've developed several server technologies, and feel very comfortable on that side of the house. I am confident in my ability to direct the server technologies we need and produce them on time.