Taking into account the designer's words, I think it is not hard to guess what characters we shall see in the second saga box.
We got Beorn, Thorin, Nori, Ori as heroes and Dori, Kili, Fili and Bofur as allies in the first box.
Thus we may expect Bard, Bombur, Balin, Dwalin, Bifur, Oin and Gloin in the second, which would leave one more spot for either Thranduil or Gwaihir (cannot think of anyone else). I find it given we shall see all the Dwarves despite the fact some of them had previously been released, Bofur and Bombur, plus the designer's arguments, pretty much make this certain.
So, which one will be the last, the great Eagle or Elven King. And which will be heroes and allies for each sphere? My guess is like this (including the previews).
Leadership - Thranduil
Tactics - Bard the Bowman
Spirit - Balin
Lore - Bombur
Leadership - Gloin
Tactics - Bifur
Spirit - Dwalin
Lore - Oin