Diana's rework is on the way—eventually
League of Legends' Diana might be the target of a mini rework, akin to Rek'Sai and Heimerdinger's updates in Patch 7.11, according to Riot's announcement earlier today.
Diana is a powerful mage that walks a fine line between assassin and diver, and her lategame burst damage rivals that of the meta's most powerful assassins. Why, then, is she never played in top-level competition? Because she lacks that one thing that League strives for in all of its champions—depth.
Yes, Diana is extraordinarily simple. Where other assassins and divers have clear methods of counterplay and a diverse portfolio of situational strategies, Diana's mechanics are very linear. She dives in with a Q and R, and she either kills the target, or she doesn't. Katarina can skirt around the battlefield to avoid danger before she bursts someone down. Rengar can choose which ability to empower to get a bonus effect that helps him in any given fight. And Diana, well, she can dive in, and she can get the kill or die trying.
That being said, simple nerfs and buffs aren't possibilities to fix her. Due to her simplicity, a buff would automatically make her OP, and a nerf would make her too weak, because all she has is flat damage. That being said, she's on deck for a small rework of her own to add a bit of complexity to her kit. That way, she'll be easier to balance, more fun to play, and overall a better champion.
Riot gave no clues on the timeframe of the rework, but at least we know it's being looked into.