We have no plans to add merchant republics, as there weren't really any on the map in the timeframe. Nomads will probably not be coming for quite some time yet as outside of raids they really only had a presence all the way to the east in Pannonia. We do have some ideas for trade routes, but it's not high priority at the moment.

Not even Londinium? I thought Londinium would have been an MR or MR similar government.

I'm not really sure what you're talking about here; I've never seen any evidence that there was any sort of mercantile or republican government in Londinium during the timeline. In fact it was probably mostly to completely abandoned during the main start date.