The Panasonic TVs do respond to TCP wake-on-LAN packets (that requires Ethernet, not wifi), so that's the way to turn them on. You can send them messages to accomplish other things like input, volume, turn off, etc.
I have never had them misbehave. Remote controllability/wake-on-lan need to be enabled in the menus.
Most TV manufacturers have a couple models for home theater integrators, which used to mean RS-485 or RS-232 interfaces to connect to fancy Crestron or Control4 systems. Those systems were several hundred dollars more, but they offered full controllability. Nowadays they seem to be adding Ethernet support throughout the product line.