Considering the vast mineral logistical problem steve may run into during the mammoth colonisation campaign I'm wondering if a mineral trading system might be a good idea. Sure yo can easily space master minerals around, but how about something like the civilian contracts system, you set up a trade at a certain location to sell a specified quantity of minerals for a certain price. Then if there's an existing contract somewhere in any empire to buy that mineral fir that price or higher then civilian freighters will pick up a load of minerals, deliver it to the specified colony and payment is automatically transferred.
This would allow empires to sell off resources they have in abundance and buy in those they don't have easy access to. Of course there significant work needed to make NPR AIs use the system properly, but for now I'm sure it could easily be tied into the normal civilian freight network without too much hassle ( maybe forget the complicated pricing system and just use a placeholder, sell one mineral for one dollar, buy 1 for 2).
Eventually this could tie into civilian mining and shipping operations, mining operations actually selling their resources onto the market, shipping companies needing to buy from the market fir shipbuilding( if all minerals aren't available on the market they could pay a premium for missing minerals to be 'found' ie just be generated). Large civilian populations should generate demand for TNEs also which should be traded accordingly.