Honestly, I normally hate the idea of obligatory group areas in non-instanced content.

However, they've already given us a genuinely workable form of that, with FATEs. Many CAN be soloed, but it's a slog, and people have frequent incentive to join in.

If they actually decided to make areas of the main game world require more than one person, I think this dev team, combined with this community, could actually pull it off.