I can only say that with my Q80T and a Panasonic ub900 player is that The player is saying 10 bit, with an LG oled B7 it was telling me 8 bit in the players settings.I do wish we could get absolute confirmation of the panel type on the Q90T. All documentation at this point does note that it has Ultimate UHD Dimming which a prior link states that this would be a true 10 bit panel. The Q80T is listed with Supreme UHD Dimming indicating the cheaper panel. My feeling is the Q90T was given the better panel but again no 100% proof at this time.
As for HDMI 2.1, I think many get carried away with it. There will never be be that much 8k content/sources to support it. Across the board many get eARC support which for me is important for audio support
One HDMI 2.1 port is plenty for most, only if you need it. I can’t imagine too many people would be buying both next gen consoles to run side by side.
I’d much rather Samsung bring support for Dolby vision as it seems to be the only manufacturer not to support it.