I think it comes down to a few small changes that would make a big impact in trading (I'm not talking increasing the profit.. making it more interesting, make finding new routes an enjoyable task that rewards people that are willing to put the time in.
It may be a gamble from FD's point of view, it's super stable at the moment, but also very boring. Make it more unstable, make the prices go up slowly with no (or very high) limits, and drop quickly. Add something to export from industrial (bring some of the Hi-Tech stuff over that's more suited to industrial) and add something to Agricultural to export.
Make traders work to find better routes, push out into the long distance stations and anarchies.