I agree with Parz3val on this one. It might make sense from a lore perspective to keep it segregated by GCs, but from a gameplay perspective it doesn't and gameplay needs to come first. PvP in FFXIV is already hardly supported and Frontlines will have a hard time changing that if people can't freely play with their friends.
Square Enix has a habit of making really great content, but with weird and inconvenient restrictions. Sometimes they need us to tell them as much so the game can be improved.