Where it gets messy for me is when trackpad locomotion is introduced in games like Pavlov. I can barely do intricate thumb movements while the same hand is steadying my rifle or performing a reload, and I can't imagine this being an accessible control scheme for the mass market.
The solution I propose is a modified version of Quell 4D's default carrot-on-a-stick mode (you hold the left trigger and extend your left arm north to move north, and so on).
Replace the controller with the HMD, and replace the trigger with a trackpad click, and now you're leaning to move and can still grab ammo off your belt without having to concentrate on where your thumb is positioned on the trackpad. Furthermore, a short press could toggle between roomscale and lean locomotion (so you don't have to think about your thumb at all), while a long press would activate roomscale as soon as you release the trackpad. An option menu item would allow you to to switch between automatic (reading your intent by how long you press), hold only, or toggle only.
I like the gunplay in Out of Ammo. It's more on the arcadey side with bullet tracers and no recoil, but for me it strikes a perfect balance of fun and challenge.