A lot of the features you mention were already there in XMPP 20 years ago. I've lost track of the standard a long time ago but I assume the rest have been added through extensions.
I think the issue is that people are adjusting what they see on screen instead of adjusting their environment (i.e. room lighting), even when they are totally able to do it.
A dark mode could make it bearable to work in poor light conditions but won't improve on the fact that it's already a non-optimal environment.