I also expect future additional Britain-linked leaders, some more conventional, but a standard two leaders per civ would bring back all the problems that separating civs from leaders solved (being able to have archaeological civs with no known leaders, being able to include leaders with multiple potential civs without designing multiple clothing sets for different civs, and being able to include leaders without having to build a whole civ just for them aka Alex andBolivar).
Splitting leaders from civs is an unambiguous massive step forward for opening design space for the game, and not only turning back on that to say every civ should have a leader, but *doubling that* to every civ needing two leaders is just about the most catastrophic takeaway possible here. Saying one of the two must be conventional would be still worse, limiting design to the civs that have traditional Great People in Traditional history. To which I say, heck no. No more linking leaders and civs.
Plus, two leaders per civ would be a massive design bottleneck. Do you expect them to go from 20-ish leaders (personas not counted) to sixty (at twice the price and in two more years) so every civ has two: or would you rather ship the Vanilla game with 10 civs?