I have been thinking the way to get an old style shooter like Quake or Unreal to work in VR without giving anyone motion sickness. Use a laser style bore sight on the weapon to avoid any weirdness with 3d cross hairs. Using the right stick to aim the weapon does not turn your view point, click the thumb stick to snap recenter your front with the weapons direction, and when you turn the weapon more than 90 degrees from your front (adjustable). Using the left stick to move sends the avatar off while the VR viewpoint remains stationary, but re syncs every second(adjustable) with the avatar or when you click a button. A small window in front of the player shows the first person aim point so they can still run an gun effectively as well as seeing the laser sight from 3rd person, horizontally the window should remain centered but rise and fall vertically with the aim point so the aim point remains the same place relative to you when you re sync. When the player is synced until they move the left thumb stick again you can use "meat hook avatars" or just show the weapon. This will allow you to play traditional FPS games with lots of jumping stairs and crouch button use, from the seated position with an ordinary game pad without any motion sickness.
If you have 360 standing VR with motion controls you dont need to worry about the snap turning, and you can use inverse kinematics to animate the avatar, but maybe just show the hands when you are synced if inverse kinematics is not convincing. The run and gun aiming window would stay close to your weapon hand, maybe still showing the weapon in your hand with an aiming portal in front of it, probably best to position the portal between the players/avatars head and the point the laser sight is hitting.
Follow this advice and traditional FPS can be ported to VR comfortably, without changing the game play design. But also allow them to be turned off in the options menu to keep the vocal minority with iron guts happy. Porting to standing VR with motion controllers will require a bit more programming especially on really old games without proper skeletal animation.