Just because they haven't been revealed doesn't mean we should assume Ghirahim and Imprisoned are the only two important people to talk about. We could say, like, "Well Ghirahim is this and Imprisoned is that but I wonder what the other 5 are going to be like or where they will rule dominance or will we fight them 1:1 sword battles just like Ghirahim"
Honestly, my theory is just that: the 7 demon tribe memebers are gonna be the 1:1, no-nonsense, sword fight battles, whereas all other bosses are gonna be typical puzzle bosses