1) Vancian casting - I may be a fan of 4e, but I missed reading my spellbook.
2) Hobbits - I like kender in Dragonlance, and mere mini-humans not at all.
3) Proficiencies - People don't read lips or brew beer anymore, and that's a shame. Just make it more flexible and/or allow people more proficiencies this time.
4) Rogues that are good a finding the traps, not just disabling them.
5) A Tarrasque that doesn't look like Godzilla.
6) Magical items that break the rules.
7) Random tables for monster encounters, treasure, and NPC personalities. Cause sometimes I have a life to live outside of D&D.
8) A single-player 5e D&D based CRPG that allows you to create your own adventure modules and content, because I've played through far more 3e characters through NWN1 than I have through 3e.
9) Potion miscibility. Because it is funny/awesome.
10) Dragonlance and Council of Wyrms, preferably in the same box.