There are many commercial solutions for home-automation systems that are based on a two wires bus both for bidirectional data and for powering the modules. The number of connected modules could be high, 100 or more.
What is the technology of those kind of buses? Are they simple half-duplex RS485? In this case, how the power can be distributed on the same wires of data? Is the protocol master/slave? In this case, the time to poll all the modules could be some seconds and the reaction of user commands is very bad.
Or are there other solutions?