Each of those actions can be done via Audio Return Channel (ARC), and perhaps most/all of them via HDMI-CEC. About 50% of the time the Chromecast Google TV we just bought can adjust the tv's audio itself (unless we are casting to it, in which case it does nothing except pops up a notice to check settings, which we have thoroughly checked).
But there's still a lot that can not be done. I change my Samsung monitor's brightness, gamma, & "lean-back" view mode multiple times a week. On my projector I switch between "quiet" & normal mode, & adjust keystone & zoom depending on position.
It'd be awesome to de-interface the TV, to create machine-to-machine interfaces that let the TV be a "dumb" screen while still being able to fiddle it's knobs. We could definitely go middle-way by returning to the tv having an "on screen display" only, some menus for configuration, but I'd love to also expand the digital controllability of these things, such that Rokus & GTVs &c can integrate with, become a comprehensive modular hub/brain for controlling the TV.