Yes, CEC can do much more, but IMO the basic requirement is to power TV on/off properly and control volume, so that I can use whichever HDMI device's remote alo

Yes, CEC can do much more, but IMO the basic requirement is to power TV on/off properly and control volume, so that I can use whichever HDMI device's remote alone. Everything should be extra. But yes it can do much more: You can program records over CEC! You can directly select broadcast service! (i.e. not just through key presses, but indeed say which channel you want) You can display some message on TV's OSD! You can discover another device's language! You can make audio 0.1% or 0.01% slower (or 1% and 0.1%? I don't remember) I don't think I've crossed any device that supports any of the command I just mentioned however. Though "Dispay some message on TV's OSD" from CEC bus would be perfectly on point based on TFA.