If you restrict lords to being able to only trade with adjacent regions you essentially require a trader if a realm is to survive. This will destroy small realms. Not everyone wants to play a trader, so requiring them is a bad idea.
I agree. Allowing traders to see the deal a bit earlier... sure, the idea might have merit, though I doubt it'd give them a significant edge and would probably just needlessly complicate lords' lives. But restricting trade in such a way? That would be utterly awful.
And any change that makes traders really important should at least be preceded by allowing priests to be traders.
Traders' range is already a significant boost, though. I don't see why they need anything more than this. Just boost the range if you deem it unsatisfying.
