... I don't think the math works out like that. There aren't 1.5KMJ or 32MJ power plants in normal Buildcraft, for one thing -- any situation requiring Diamond Pipes means you're actively condensing power from multiple sources or using fairly specialized mods, and the most common power sources all fit on Stone Pipe. Even if you needed an always-on communal power plant, it'd make more sense to have two stone pipes to each 'house' with a single gold pipe condensing node per house.
It is true there aren't typically massive plants in BC alone, but the capability is still there even with no other mods. More importantly though, please show me ONE person or server that uses BC alone as their only MJ using system. A mod designer with dozens of mods based on his mod needs to take such things into consideration or someone will come along and replace him.
It would not make sense, even if cheaper, to have 2 stone pipes too each house because that would mean massive tunnels cluttering the underground of your city to accommodate the multitude of pipes you have to run in parallel. Doubly so if you put the plant on the outskirts as that would mean an initial tunnel housing 96 pipes. Even diamond pipes would be annoying in that situation as you would need 6 of them for all 48 plots. Also expansion would be a massive undertaking instead of a minor one. Basically it would just never happen because people would immediately recognize the logistical issues and give up.
That'd be... really hard to handle, especially with how poorly minecraft handles saving data that isn't tied to its internal save structure.
I don't know about the save thing, but what I am describing is just a node network which I think it's what they plan to use anyway. As a matter of fact the only thing they should need to do is add a new (affordable) pipe that conducts something outrageous like 8192 MJ, but then make it so absolutely the only thing it is able to connect to is the special diamond pipe. Aside from that it would be behave precisely like the be pipes will behave anyway.
Thinking about it more, the special diamond pipe (which should also conduct 8192MJ) should only connect to three things... The long distance pipes, another special pipe, or diamond pipes, and then only two diamond pipes at a time. That would mean you would need at least 1 special diamond pipe for every 512MJ going into the system in addition to the one per location you pull power out at (and more if pulling out more than 512 at a single location).
Also keep in mind this is just an idea. I am not trying to say anyone is stupid or this is the only way to do things. I just saw some teasers from EDX the other day (above ground power cables like the ones we have in real life + what looked like a small transformer like at the end of your block) and it inspired me to think about power transmission in minecraft in a different way.
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