Two additions

Heat pipes would be super useful, because who doesn't want a room full of reactors working optimally and pumping their heat out to another factory building to turn into steam and electricity ;)

And I know there's already circuit network things but they take up an input/output slot it'd be useful to connect internally to the substation and externally to the building as an extra route that doesn't block off for pipes, belts or chests even if it's ridiculously slow (like once every minute) while if you want more dedicated speed you have to use a input/output slot

So I actually put some thought into how this could be done last night. I was thinking of making a pull request. I think it could be done in a lot the same way as fluid transfer. Since the game has no heat pump concept (and such concepts aren't really viable in this context) what I think I would have it do is be locked in "balance" mode where the two pipes basically equalize once per update, though the warmer pipe stays slightly warmer still to introduce the "inefficiency" that the heat pipes are supposed to have.