I imagine their interest in parallel channels is partly to avoid any motion artifacts where the visible image and the mask channel would diverge between the sample intervals. I think this is why sub-pixel color filters have won out over filter-wheel cameras in general, i.e. where a monochrome sensor reads the R, G, B fields in sequence.

But given that it comes from Netflix, it is probably also constrained by wanting to work with commodity cameras and optics. It seems they would want techniques that can scale to many productions at once with low marginal cost.