sorry for the late reply. A few answers on top of my head…
Probably the chromaticity-linear approach (our “ground truth”) and a proper SDR/HDR match. Without any HDR display, it is hard to say. Jed did some interesting SDR/HDR comparisons in this thread though.
Yes, we may be back to square one because of that ? A look embedded in the Display Transform.
Probably missing a “gotcha” that per-channel is the root of evil ? It does not respect the RGB ratios of the colors used by distorting hue, saturation and luminance. I have tried to describe this behaviour here.
I think Daniele answered this question in this thread. And rgbDT, because of its per-channel nature would probably need a new set of primaries to be invented. We did think about AP2, just like in this thread (even if that’s for a totally different purpose) !
I may add that with a flexible architecture allowing for swappable Display Transforms, people could innovate and use rgbDT as an alternative if they wanted to.