This is how I would detect jumps: I am NOT a vr dev but it's clear that the controllers and headset have motion sensors in them so.... let people jump and when they land you check if the motion sensor captured free fall movement before that. If it did, you register this as a legit jump and they crossed the gap. If they didn't they actually walked over lava/acid and need to take damage or whatever. I know this brings in a delay that ruins immersion a bit when you don't jump but the player that actually jumps will just cross the gap. Idk this just crossed my mind and I thought i'd share it. Cool stuff!
It really depends on the headset, but I think that most of current ones don't have a motion sensor, they are just located using either lighthouses, sensors or cameras. But you could still get the velocity from that. The bigger problem is that delay introduced and possible false positives and true negatives and that may lead to player's frustration. While I have lots of things that I want to add to the game, I will have to drop some ideas or at least leave them until an update.