TL;DRA "network-mask" value on the electric pole prototype that masks the auto-wire feature when placing poles in range of each other, or something similar, to allow creating pole entities that automatically enable overlapping electrical networks.
What ?The technical aspect is explained in the TL;DR. The first thing I would do is create something in a mod, probably called a "Transmission Pole", that has a separate mask from all the other poles, and a "Service Pole" that connects to both masks (thus providing the interface between the transmission and service networks).
Why ?There's a lot of sense to using an integrated feature like this when creating overlapping electrical networks, because we want to take advantage of all of the convenience functions that are built into placing electric poles -- running with the mouse button held down, or resetting lines by removing and replacing a pole, etc. -- and there are definite uses for connecting regions with a separate network that go through some other region that you don't necessarily want to be connected. Generally people agree the electrical system could use a little flavor, and this might be an easy addition that I know I would take advantage of in a mod immediately. It would also help to preserve overlapping networks when using blueprints.