A sensor that reads the outdoor temperature for example and displays it inside on a LCD. Or other data like wind speed, motion, light/dark sensor, etc... and use this to trigger events in the house.

That would indeed be a possibility. That would unfortunately mean a seperate network inside, one at the front outside and one in the back outside. Then the sensors of outside would not be able to communicate to sensors inside directly. Would be cool if you just could have repeaters wired (with ethernet or rs485 for example) so everything is on the same network.

Is it possible to have a wired repeater/relay? The problem is that the signal of sensors and repeaters outside my house will not penetrate the wall (shielded isolation in outside wall, windows with some sort of metalic foil). I do however have several wired network cable outside I could use to make a wired repeater. Is this possible?