Hey,
just wanted to chime in some feedback from our CTO about HDR and SDR.
We generally do our first hero grade in SDR where we try to have our movie as beautiful as it can be. And when we move to the HDR room, we kinda expect to see something similar as a starting point. The worst that has happened is when HDR looks completely different from SDR in an uncontrolled way (this may be due to many reasons). And as a client, we expect as a starting point to have a respect of the creative intent. Rather than flames or skies changing colours.
I’ll quote @daniele and @joachim.zell from meeting#6 :
I don’t think nobody really means it should only go to 100 Nits and be like, literally the same, appearance.
But what I saw just by working with clients, they feel so comfortable when they walk from the SDR room to the HDR room, and recognize the imagery, then they say, Oh, good, I mean, in a good, in a good facility here, but Now show us what else we can do can be.
Not sure if it means preserving appearance or not. 
But I like this quote from Colorfront :
Will SDR look the same as HDR? Is the look of the image maintained ?
Regards,
Chris