I'd like to see a challenge system, and also improve anti-cheats.
I agree with you on those two.
I lowkey miss the challenges we had on java. They basically made you play game modes you usually didn't play, and sometimes you find out how fun they could be and then you start playing them more, at least, that's what happened for me.
And as for the anti-cheat system, its being improved each day. The staff is working hard to make Sentinel work better, and eventually, it will be better then ever.
Though I would love to see more non-pvp modes, since that's what the casual players are after. Just look at POF as an example.