They should add more stuff to the nether, caves and go back to original combat. And make it so Wolves can eat meat off the ground.

New mobs

they should add different flavoured cakes!

- to fix mc
-fix the bosses
-fix combat
-fix lagggg
-fix the endgame grind

any questions?

One thing I need is some lag suppression.

I need it to stop lagging my server with unoptimized entity ticks lol. 1.14.3 is a nightmare for my server. That said, in terms of in-game features... I'd like nether and end biomes, cave biomes, more overworld biomes like redwood forests, cherry tree woods, etc. New dungeons, challenges in all dimensions. Get some asian themed stuff. Make it so redstone levers switch when they receive a signal. similar for buttons. When repeaters/comparators get powered from the bottom they change states. make icebergs interesting- maybe with penguin colonies, seals. Add more to villagers- the current implementation feels incomplete. Make them more like millenaire. add observer burnout, similar to the sort with redstone torches. Make bats not stupid- give them proper AI and things to do. Make it so passive mobs behave like the ought to instead of just wandering: pigs should wallow in mud, chickens should peck, cows should graze, sheep should jump on things. Llamas should do... whatever llamas do. Turtles don't beach themselves all the time. Make potion potency decrease progressively with time as it wears off. add herobrine. Make proper, functioning pillager outposts where pillagers actually do things. Add slight variation to all mobs in terms of speed, health, attack rate/damage. Just to make the game feel a little more exciting and alive. Remove the cooldown on attacking, at least with swords and fists. Let lecterns display maps. make pets less suicidal, and possibly upgradable or trainable. Make passive mobs attack or run when hit. Except sheep, which should panic, faint, and fall over occasionally. Make fox sounds less annoying. I want to love foxes. But I can't. Add random shooting stars to the skymap. Add seasons that impact snow, rain, crop growth, spawn rates, etc. Add a native in-game mod manager. Add chat link previews. Allow the chat location to be changed, or even displayed in a separate window. Allow carpets to be placed on glass panes as curtains. Use levitating potion on a carpet to make it fly. Increase donkey chest size. Add an ingame minimap and waypoints, which can be disabled or managed by server owners. Add an in-game screenshot-sharing platform. Add ingame friend system to join servers your friends are on and chat with them at any time, as well as server administrators. Voice calls optional. Make eggs cookable. Thrown snowballs inflict brief, mild slowness on targets. Take damage swimming in frozen ocean. Add giant squids, which may attack boats. Dolphins may attack them. And lots more. I didnt think I'd go on this much

Those sound more like general things that should be added, but I do hope that they would be added soon (maybe putting it on the Minecraft Feedback site with more details would be good)