Sry if I was a bit unclear, let me precise what I meant (and as with everything on forums, if I'm wrong, please correct):
Yes, todays sticks are USB. The FFB protocol (Aka, the way FFB commands are transmitted) is still the old midi protocol from what I was able to read about it. That's due to the history of the technology which was introduced on the old midi/gameport 15-pin ports which back then were used for sticks and midi devices. Like on this beast which I still have around here somewhere:
What they did was use the midi capabilities of the port, which the sticks didn't use anyways, to transmit the control commands for the FFB motors over it.
I'm assuming right now that with todays FFB USB sticks, that didn't change. It's still midi commands that are being sent to the device.
(Addendum: DirectX is just a standardized layer that generates those midi commands so you don't have to directly tell the device how to run its motors. It's not replacing the actual protocol from what I understand about it. Corrections of course welcome if I got it wrong.)
About the software device: Yes, you could of course do that. But what you would really want is make use of the information in a haptical way (aka, you want to feel something, not just display a number on your screen somewhere). Hence the idea to put an Arduino device behind it which you can use to put the FFB information into effect.
A software device to log the commands would be a good first step though. I'm not privy to Windows Device Driver Developement, maybe somebody else can comment on the feasibility of it.