Personally, I like the idea of expanding the Edinburgh system because it gives more meaning to the Gaians. Putting tradelanes, usually in major populations, is a surefire way to make it seem Gaia is getting closer to being invaded. Plus if it connects Ayr, it puts an even BIGGER bullseye there. Of course, the logic could be that Bretonia has waited this long because of the Gaians and their attacks slowing things down - if it was completely safe, it'd be done already.
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That being said, here's my idea for a future Bretonian system, situated on the map below Manchester, and connected to it, Salisbury, and Cambridge.
My idea: with the war going on, Bretonia needs more ships, more resources, etc, etc. A couple years back, a jumphole in Cambridge became phase-aligned to the barren, but mineral rich, Swansea system. It had been previously unexplored because it was not easily accessible and, lacking any stars, it was overlooked on larger scale exploration. BMM established some miners to get at the band of minerals amidst the Barrier at the time.
With the war escalating, the government decided they needed to act. A shipyard was constructed to build ships there and move them directly to Salisbury for the war effort. Bowex established a depot to import the necessary components and combine them with the local materials (beryllium and niobium both appear in the Barrier elsewhere, not sure if it's feasible, or they might just be in less accessible forms of rock).
Gateway was allowed to construct a depot of their own; They generally ship the extra metals from the area to the civilian market and bring in additional components for the shipyard. An area had also been identified that might be a good spot for a future jumpgate. Currently, however, it's far away.
Unfortunately, not only was there a jumphole to Cambridge, letting Mollys and the occasional Corsair in, but a new one has recently become aligned to Manchester. Gaians from Holmfirth, disgusted by the newly built operations, launch raids from there. At best they could fly through, disrupt things, and escape to the friendly Cambridge system, where they have significant support.
Anyway, just an idea, please expand on it if you'd like and make Bretonia awesomer. :D