I think Da Vinci's infodump on Babylonia and Merlin's lecture on GoA about True Aether are teasings about what LB6 will be about
Regarding Beryl's servant, can't remember if it was LB2 or another one that confirmed the servant the crypters summoned is restricted to belonging to their territories (which means, Beryl's servant should be from the British Islands). But nothing really restrics them from making contracts with other servants on site so...