This reminds me of what I see as a typical oil refinery layout:
Assuming that underground pipes are considered to be a single segment, that layout boils down to 5 sets of this:
One thing becomes immediately apparent, which is that there's going to be tons of junctions in extremely close proximity. Since junctions are going to be the intensive part of the new pipe system, I see a (relatively) simple solution to the problem: Combine junctions.
For the last image, instead of having eight 3-way junctions, what if it was two 6-way junctions? All of a sudden, 75% of the junctions are gone, and it's went from 24 connections to 12. Assuming this merging only happens on pipe additions/removals to that pipe network, it should in theory massively improve the performance of the system that is being proposed, at the cost of a CPU hit when modifying pipe networks as it tries to work out how to merge junctions nicely.
For the image at the end of FFF 260, it would go from three junctions (3+3+4 way) to one 6-way, going from 10 connections to 6. Not as much of an improvement, but that's a theoretical scenario when my realistic example has a far bigger benefit. One way to look at it, is that every merger removes one junction and two connections.
The problem I foresee is save-load stability, since it would be horribly inefficient to break apart all junctions and remake them on a single pipe addition. Other than that, I can't see this addition performing worse than the current proposition in FFF 260, since pipe networks are typically left alone.
