Let's hope that 4K will became the bottom standard workflow at least for features, resulting in 4K DCP being the norm, rather than exception :)
It is very uncommon to see DCP with those bitrates today, in fact I can't remember anyone.
And still, no reason to use a less than 4K workflow other than costs.
I don't understand the blu ray comparison, it doesn't make any sense, can you elaborate?
DCP are *always and only* 12bit 4:4:4 encoded in JPEG 2000 with variable or fixed bitrate, at 2K or 4K resolution. I repeat there is no reason to use a sub 4K worflow in 2018 and to not release it as a 4K DCP, at least speaking about feature.
Who do you think will be the first director to use the new camera?
I really do not understand what You're talking about:
HDR and dynamic range are not related to resolution, You do not waste anything using a 4K (or better) pipeline in order to finish in 4K, rater resolution, colors and dynamic range they all go together, You can see and example of it with ECLAIRCOLOR platform :)