In one of Arri’s papers covering the basics of HDR, this stood out the most:
Should I grade HDR or SDR first?
There is no consensus in the industry yet, which color grading strategy is better. Both approaches are being used today by HDR productions. The advantage of first grading for SDR is that most displays currently are still SDR, so you are grading first for the largest audience, and then making an HDR trim pass to also have an HDR deliverable. The advantage of first grading for HDR is that we have often found that this in turn also makes for a better SDR grade. However, the client who has seen the HDR will not be happy with the SDR. [italics my own] 😬