There are working on cross server instancing, for OPR initially but this can be pushed out to invasions, dungeons etc and yes I nice persistent War map between servers that resets weekly, akin to GW2 WvW or something like that.
So smaller companies can get the a decent number of participants. While I like invasions, I most certainly do not like the damage that occurs to crafting stations etc if you fail to defend.
It may be technically hosted on a separate physical/logical server when in play, but itβs still based on the population from one box, not cross server.