First of all........ Double-Jump and Wall jump, just think of what obstacle courses will become!, would be great
Second: a Catme button, cats rock (also skele me etc)
Third: Blockland beta death! i loved it how you turned into a skeleton and turned to bits, but make it so you dont get skeled! that would look great! (on the subject of dying, kill yourself with /timescale 0.5 ;)
Fourth: A cookie monster shirt
Fifth: When you have no item out and click, do a punch animation that does dmg to players in a dm and when not in a dm a push animation
Sixth A bit stupid, but heres goes... Pets. Yes pets, like a little kitty that follows your char around and when gets too far away respawns next to you, and has no collision, ive seen it done before with bots, just change the models.
Seventh: A two seater sports car (bloko style)
Eighth: Good old jail function from RTB, nothing like a caged noob!
Seventh: Third person camera
An last of all.. A GODDAMN HEALTH BAR!!!!
(Oh and i AM aware that half of these have been suggested, and i am aware that they will never, ever be made, but oh well)