Mages should have to deal with mana management
Nerfing mana items could potentially bring mana management back into league, even slightly. Instead of taliyah q'ing the wave twice, running back to her tower (Maybe roaming if 6), and then repeating, she will have to take more risks and perhaps make a more interactive laning experience. It could also mean, that without the ability to 24/7 spam abilities to clear waves asap, she could potentially spend less time roaming botlane, so that the current "4 v 2" botlane crap doesn't happen as often.
I played back in the early seasons when mana management was a large part of league, now adays riot has given so many tools to mana hungry champs. So Maybe I'm a little bias, but I see Mana management as a way to express a players skill, which I think league is lacking atm.