VR dev here - all of the vr projects I've worked on have had a developer only "screen mode" that lets you move the character/camera and do basic interactions without being in VR. These modes / player controllers are made to make development and testing easier and faster. If you're just testing some basic scripting or a world element, you don't need to be looking at it in VR all of the time to do iterations, so not having to pick up your headset and switch from screen to VR and back a million times a day is helpful!
Many times these modes are used in conjunction with hotkeys / cheats to perform basic stuff - like a keypress could automatically act like holding your glove out and letting it go could act like the "wrist flick" that brings objects your way. Taking out a clip and reloading could be mapped to a keypress. An on-screen cursor could take the place of aiming, grab mechanics could be automated and mapped to a generic use etc.
I've played about 2 hours of Alyx so far, and depending on how hacky a mod could get (access core features like calling reload on the gun, advancing the next stage of a puzzle, or enabling something to be picked up with a cursor instead of two hands), it'd be possible to do a non-vr mod, but it still wouldn't *feel* like playing the game the way it was meant to be played would feel. It would be compromised and while you might be able to play through it, it'd likely feel hobbled or *not as good*, etc. But conceivably possible? Probably.
