I like VR first person shooters.
With all this attention on developing haptic feedback controllers for gun recoil, frames for shouldered rifles, and omnidirectional treadmills, the one thing nobody seems to be working on that I really, really want is a controller trigger that has a crisp wall and distinct reset. The mushy, vague controller trigger is a huge barrier to immersion. More than a recoiling controller, this mod would take the immersion over the top for anybody who shoots.
I'm thinking maybe a mechanical trigger shoe? You would have to calibrate the shoe the actuation point of the trigger. Then there's the matter of what kind of mechanism would do the trick? Maybe a modified mechanical keyboard switch - e.g. Cherry MX, Gateron, Zeal PC ... with beefier springs. You might not get a 4-5 lb pull but you can definitely get some trigger feedback.