When you move forward in VR, you experience a slight "hit" to your stomach at the start of your motion, but it's not continuous. Motion along a forward or backwards vector isn't bad. What is killer is yaw rotation. That alone is probably the biggest challenge facing VR.
I wonder if the classic Resident Evil tank movement would be a solution for some games since you rotate before you start moving forward, and to rotate you would need to turn your head left or right. I haven't tried VR but turning around using a controller without your head actually moving seems like it wouldn't be a very fun experience
for your stomach