> Much higher performance ethernet.

Depends what performance you are after. Ethernet isn't rated for safety critical stuff. It doesn't provide mechanisms for packet loss detection, and in most cases is pretty shit at flow control.

Ethernet is also shit for small sensors/actuators. There are lots of low bandwidth devices that need power and comms, ethernet isn't designed for that. having to route 2 pairs of cables to everything in a star pattern is really impractical.

Its probably ok for linking different zones, of non critical stuff. But running PoE? for all but specialist things, that sounds frankly stupid.