In the interest of encouraging socializing and trade, there should be some kind of Realm-built structure (only one per Realm) that can be ported to from any Realm-controlled Thingwall. I think by default it should apply something along the lines of the visitor debuff in a certain radius, to enforce a "safe zone" for trade and assorted revelry.
Maybe there would be a distinction between "citizens" of the Realm (someone whose hearth fire has been within the boundaries for a certain amount of time) and those who are not, with different debuff restrictions accordingly.