I had an idea for the silk road (that is sat on my "someday, maybe" list of things to do) which was to represent the mercantile element using the merchant republic dynamics - as you can actually have inland tradeposts, by creating them in the province history. You can't access them through the province panel, but you can by moving to next holding. The key difficulty was positioning the capital next to a body of water so you could have a port.
Haven't fiddled enough to see if it is possible to dynamically create new trade posts or anything.
Haven't fiddled enough to see if it is possible to dynamically create new trade posts or anything.