Well, my idea wasn't really for a long work day, but more for just walking in a virtual park or playing paint ball with your friend that moved to japan or something like that. It's meant purely for an hour or three of quick games.
Haven't spent much time in immersive environments, have you? You may want to research "simulator sickness"; there's also a related issue (can't remember the name right now) in which after being in an immersive environment for a long period of time, then exiting, the "real" environment becomes somewhat "unreal" - they make pilots take a period of time off of flying after long sessions in full motion flight simulators. The level of immersion is the main issue; the more immersed you are (and the longer you spend immersed), the greater the effect. Simulator sickness, however, is another thing - everything from lag to sounds to optics focus, etc - plays into it; headaches, nausea, etc are common.
Also, I personally think it would feel more immersive to actually walk in the environment rather then sit with joysticks. I can see that being better for longer sessions of work and such, but as far as for gaming, the only difference with that system that I notice from regular gaming is the chair and having an enclosure around the user and the screen.
You would think, but it isn't necessarily true; I suppose if you are trying to simulate earth-based (or similar) environments, then sure - keeping your "feet on the ground" would be wanted. You may want to look into what the US Department of Defense has done with their "Dismounted Soldier" project; their goals are kinda similar, wanting to train soldiers in varying terrain, etc.
As far as the Flostation is concerned, being in the chair was meant to simulate a gravity free environment. By supporting the body in the pose they designed (and in a chair that supposedly was very posh and comfortable - these things were handmade and very expensive), which like I said was a patented combination of the "zero gravity" pose and some pose for yoga - supposedly the outside world "went away" for the most part. This, coupled with the special display (essentially an XGA projector projected on the outside of the sphere the display; it was spherically warped by optics or software, such that inside the sphere, the back projected image was perceived as "flat", but it still surrounded your peripheral vision area - it was actually a pretty neat hack, giving the benefits of a large FOV HMD and monitor all in one, at a lower cost), and the motion platform system (yaw/pitch/roll mainly), along with other transducers (bass shakers) allowed for a very interesting experience.
The system originally was designed out of the guy's garage, then he got a NASA grant to expand it and use it for astronaut training; it didn't go much beyond the prototype phase (but the prototypes did tour the country to various conference venues).
I don't mean to say that it's not a bad idea, just not the same kind of immersion that I want.
As for the hydralic/pneumatic system as well as the air muscle, I'd be afraid of what happens if something goes wrong. Hydralics don't give in all that easy, and if someone's not expecting it, a sudden jolt from the game engine could physically harm someone, which is NOT a good thing from a company's perspective. Lawsuits and such being what I mean.
A valid thing to think about; if such a thing is on your mind, then pneumatics running a low pressure (or being actuated by servos, instead of a pump system) would be best. Pneumatics have a springyness to them that would be more suited to the need. You could potentially do something with motors and gearboxes, but you would need to make sure that everything was either back-driveable and/or clutched, which would introduce more mechanical complexity. It might be possible to do something with cables and slip-clutched winch mechanisms attached to gear-motor servos...
I would need something that's soft as far as strength goes, but strong enough to make you feel that you're walking up a hill, rather then just walking forward.
Something you might also look into are 2 dimensional treadmills. Essentially they consist of two treadmills that overlap each other, and the belts are composed of many little rollers/wheels at perpendicular angles to the direction of travel. When you walk on them at an angle, the motion is translated via friction to cause both treadmills to move in proportion the vector sum of the direction being moved. You then allow for motors to backdrive the treadmill, and then mount the whole unit on a motion platform (to allow you to tilt it)...
Thanks for the suggestions though I appreciate it, and I intend on going forward with this still XD Just need to find the right motor/pressure system.
Good luck with the project; it won't be easy, but it will be rewarding (and if you have never been in a fully immersed virtual environment - you may be in for a treat!)...