It's worth noting that DP 1.4 can actually do 4K at 120Hz, whereas no consumer graphics card currently supports HDMI 2.1 output for 4K 60+Hz. HDMI 2.1 is pointless for a PC monitor ATM, and it is likely that no display controller currently supports both HDMI 2.1 and DisplayPort 1.4 concurrently.
This is a monitor for the PC market, and its value comes from 4K 120Hz support that's usable today, its low colour deviation value, and its high DCI-P3 coverage.
As cool as full HDMI 2.1 is, we need GPUs that support it. They will likely come later this year, but they are not gonna be ready until ??? (my guess is July/August) for next-gen Nvidia.
This is not to say that I think the price is worth it, I'm just saying that you are expecting a lot if you want DisplayPort 1.4 and HDMI 2.1.