I really hope Valkyrie has something more than just VR dogfighting because flying in circles, playing the "who-can-get-behind-who-first" game gets old fast.
What made the Descent series so much fun was that it took place in an enclosed environment, with obstacles and other environmental effects to consider.
My ultimate "space sim" would take place in Karl Schroeder's Virga environment, which is a giant air-filled bubble in zero-g. Speed and sight-distance can be realistic, air resistance makes maneuvering fun, and you can have lots of obstacles if desired.
Though I'm hoping that there will be some decent plain old flight simulators coming out with Rift support. That would be a good reason to upgrade my gaming system.