I'd like to see my Orks brought up to date, but I would be happier to see the Eldar Aspect Warriors get proper treatment. I think they have aged well, but I want to see Finecast stamped out of existence and the non-wraith Eldar are one of the biggest bastions of that horrible stuff. I mean, I was moaning about Wraithguard being so expensive in metal and Jetbikes being so outdated until they were updated so I'd like to see the more traditional Eldar units get updated. Oh, and please give Shining Spears a proper kit. I never considered their conversion kit to be a proper kit, they barely look more than fancy Guardians to me. It always felt to me that they were just an afterthought and need more development.
I'd also love to see plastic Vespid. More agile and spindly but hopefully looking less cone-headed. Their concpt art was amazing but the models we got looked a bit goofy due to the heads.
Over all I'd love to see more Mechanicus stuff obviously but I feel less than neglected with the rapid release of new kits. There's still plenty of room for me to expand my army so the only think I could ask for is an elite infantry kit that could make the Archaeopter Transvector viable.