Another vote for Elite Dangerous. It certainly has good Trading system, background simulation has it's failings but potential is great and it already works well enough. Also the starmap route tool was a horrible mess last time I tried it, but idea is good on that too.
My personal interest about Trading is that it causes reliable Merchant routes where I can hunt. So logical changes in economy and pricing ia what I'd like to see. Also good enough routes for traders so that they take the risk willingly.