I feel like a lot of champion abilities would make for really good items

So I've always liked Kha'Zix as an Assassin because his gameplay and Assassination patterns is dependent on the state the enemy is in; his Q is at its strongest if the target is isolated, perfect for an Assassin.

And then you have a couple items like Frozen Mallet or Warmog's Armor that pretty clearly share passives with certain champions in the game.

With these two thoughts in mind, I honestly believe the isolation mechanic to be an incredibly healthy yet potentially powerful tool that Assassins as a whole should take advantage of without necessarily breaking them. An item with the Isolation passive and an effect similar to Kha'Zix's Q or Duskblade would be a good addition to the game.

This got me thinking of more champions and any passives that would make for functionally niche but valuable items. Stuff like getting a small heal after hitting a certain number of targets with your spells, or a Support item that lets you tag along with other people's recalls. A lot of really good ideas already exist on champions that could increase item diversity in the game.