Since GD is mainly ignored by Riot One thing I've hated on Diana is how her ult resets. Its not an immediate reset, if you notice when you land your Q, and ult there is still a downtime for the ult to come back up which is really annoying when trying to do long range engages. (Q to minion -> R to minion -> R again to the enemy champ catching them off guard) Its too slow for her, but that just my opinion.
Save one of my most favorite champions, save 
Fellow diana main here.
I agree it'd be cool if you could do this, but I think the delay is what allows you to "anticipate the q" (hit r before your q lands): if your q lands in the .5 seconds after your r lands, your r will actually reset, even though your r hit before your q.
I think diana's got some bigger problems than that, though. I made a thread about it a while back.
I always thought the big problem was what I considered the unecessary nerf to her Q debuff after ulting. She used to be able to just dash through crowds doing moderate damage to each step to get to her quarry, and then they took it away.
Then Yasuo came out and got that as a shorter-ranged normal ability with a lower cooldown and no mana cost.
