I like your idea, but this architecture will not work as there is would need to be a switch to manage the traffic between the three machines connected to the 10GbE card (Lion Server, Final Cut, and Mac). Although point-to-point links between machines is possible with slower versions of Ethernet, the new 10GbE standard only allows point-to-point links with switches in between.
This limitation puts 10GbE out of reach for many as the network adapter may only cost US$900, a 25-port switch can easily cost US$15,000. On the other hand, depending on the work profile for your business, a full return on investment could be achieved over the course of the year or even on a single project.
P.S.: Although it's not in the standard, I would not be surprised if the industry drafts an updated standard for point-to-point operation for 10GbE in the future as this technology becomes more widespread. I welcome other thoughts from the community on this question.
Although a single point-to-point connection between two machines should be possible, to implement a SAN with more than 2 machines, you really need a fibre channel switch. See http://www.apple.com/xsan/whatisxsan.html
Please let me know how you proceed.