As for E4 types, I'd like to see Fire, Water and Grass. I don't really mind about the fourth, although perhaps Flying would make sense if we were to look at the traditional elements. Something I'd like, however, is that if Fire, Water, and Grass appear in the E4, or as gyms, then I think the ace should be the fully evolved starter of the type. It shows us that other people actually have them, whilst also adding an extra - albeit small - dimension to the characters, perhaps they could tell us a little bit about their journey, how they started off as we did with their starter, overcame challenges, etc, until they became a gym leader / E4 member.
As for the champion, if BLANK / Normal is going to become a thing (slowly accepting it...) then a Normal champion sounds like a good idea to me, being diverse whilst having a core, too. For instance, a fully evolved Helioptile and Litleo (if they keep their /Normal typings, which I doubt and hope not), maybe a Flier... (Then, using older Pokemon as examples) Girafarig, Sawsbuck, and a Bibarel... OF DOOM.