I would love if there was an open 4K HDR TV but I think only a very niche audience actually cares about this so most manufacturers will not see a market opportunity
For example, can you stream Netflix @ 4K via RasPi? I assume no, due to super strict DRM.
It is a little bit surprising to me that the big streaming companies have not creating an open source operating system (similar to Android) that can be used by manuf to create TVs. Then, smaller manuf can find ways to offer bloatware- / adware-free options. Maybe this already exists, and this comment makes no sense!
HDR and OLED are available in some monitor models, but to my knowledge there aren't any 55" monitors with HDR and OLED, and especially eARC.