To be quite honest, I think the new mac pro's design is on the ugly side from an internal standpoint. There are existing standards for things like small form factor graphics interface, like MXM, that seem like they would work much better than apple's variant which requires a rather frail looking connector between the graphics cards and the I/O card. Though I imagine one of the problems there is that it would be much harder for Apple to keep people from purchasing a third-party video card two years down the road when the current boards start getting long in the tooth.