KNX, which is a popular standard in European countries, is almost non-existent here, and imported switches are expensive.
OneWire protocol might be possible, but then again, not sure how many actually support that either.
There are some projects online like:
A complete solution for easy-to-use and affordable wired home automation
www.crowdsupply.com
And even some upcoming ones like:
Open source, flexible, modular hardware modules with Home Assistant compatibility for any of your automation needs
www.crowdsupply.com
Right now, GetWired looks to be the most promising option. Aside from that, I suppose the best way would be to just have Ethernet wires to all rooms in a house and hope there’s some standard in the future like GetWired which can act as a hub per room and communicate to a local HA instance using Ethernet.
Of course, a smart home should be “smart”, so in case of failures, manual overrides are a must, whether that be using a 2 state relay, or some other method 
There are many reasons one would want to build wired home automation, so please don’t say in the thread to go for wireless.
