the mere fact of linear DNG existence shows that flow is = demosaick -> prophoto/g1 -> (wb, camera profiles/hue twists, curves, NR, sharpening, etc)
Well, actually, demosaic -> (WB/camera profile part 1) -> prophoto -> camera profile part 2, curves, etc
The camera profile is the core of getting to proPhoto (no matrix, no proPhoto), but parts of the camera profile are also post proPhoto. E.g., the tables, which are effectively in proPhoto gamma 1 space
However, I'm not sure what the point of this is, other than academic interest - where ever the WB is in the chain, it's probably going to blow out if you use a unity matrix - many raw formats (DNG itself is a good example) encode WB as an XY point. If the matrix doesn't take you to a correct XY, and a unity matrix sure won't, then WB is guaranteed to blow out in that case. If WB is encoded as sensor relative rather than XY, then you might be ok.
Sandy