Well, there are those of us who were playing this kind of game and liked it. Though for FFXIV in particular, participating in overworld PvP should be purely optional same as it's purely optional right now. Unless you or your FC is flagged for PvP, you'll be fine.
Speaking from experience (I led a small-ish clan in Lineage II for a few years, and we managed to at one time or another conquer every castle but the major ones of Aden and Rune, chiefly because I knew how to make friends): That doesn't happen. Inter-FC politics is enough to make sure the most steadfast alliances eventually fall apart. People are people, after all.
Besides, no idea why a cross-server FC would have any bearing here. "Travellers" should be excluded from server PvP by default, to make sure each of them has the chance to develop their own political landscape. I mean, they're free to make characters on different servers, and level and equip them there, but they can still be only on one server at a time. So the same village they conquer on Phoenix, they can't defend on Alpha, Lich, Odin, Raiden, Shiva, Twintania or Zodiark.
