>>332510701
Well let's say I meant surely as in "under the hypothetical situation in which he does everything right, although that might be unlikely."

I think there could be ways to mitigate drift to an extent through some affordances in software and making assumptions about the system. For example we know that you can't bend you knees more than 180 degrees out, so we could cancel out drift when the shin would move beyond what it should. We also know the shin can't bend into the negative orientation such that your shin would end up in your thigh, so we could do compensation there too. There might be other things we can assume and do for the other bones, especially when we have the headset and hands as absolute things to work off of. The ground as well if you calibrated it correctly in SteamVR.

I'm not sure about the specific positioning problem you're talking about. In theory, we don't need to position the IMUs specifically because they measure the same rotational values no matter where they are on the limb. If your leg is straight and it measures a 0 degree rotation at the base of your shin, it's still going to measure that at the top. 

The only bone that a skeletal model reference would help with is the hip, since that's not directly connected to your head. I'm assuming it's not going to be able to estimate hip position at all if you do something like move your head side to side while keeping everything still. It'll use a model like how the DK1 use a neck model to better approximate head turning. For the hips it'd be the same thing, but probably it's not going to be precise tracking even if you very carefully set it up and calibrated it, so you probably wouldn't need to be precise about positioning it either. 

>I'm not super familiar with how good IMUs are at judging movement
It really depends on the IMU. I don't know if the one he'll use is good, but IMUs in 3DOF headsets have been able to not drift for huge time windows before.