Lump me in with the "would like a warlord please" group.
Not sure if we need a devoted summoner, but, it would be nice if more than just druids actually got summoning spells outside of a couple quite high level ones. I've played a summoner wizard in every edition but, I can't in 5e, so, yeah, I'd like to see "summon monster" make a comeback.
I'd love to see some work done with fighters. The thing is, "Fighter" as a class is SO broad, that it pretty much covers many archetypes, but, it really shows its flaws if you actually try to apply it. I mean a Knight, for example, should have numerous social skills and probably gain some sort of class based bonuses on social interaction. But, a fighter doesn't get any of that. But, if you say you want to make a knight, everyone tells you to just make a fighter.
Which tends to make all the "fighting man" archetypes really, really bland and far too similar.
I'd like to see "Fighter" as a class actually go away and then break down "Fighter" into a number of full classes based on archetypes - the brute fighter, the smart fighter, the swashbuckling fighter, the magic fighter, etc. To me, the base chassis of "fighter" just isn't getting it done.