This is obviously a massive change to the laning patterns of TONS of different champions, and making such a drastic change like this all at once seems really dangerous.
Just thinking about one of my mains, LeBlanc, the fact that my Q draws minion aggro is a HUGE change to the way I would play most lanes.
My concern is that Riot really hasn't thought these changes through, especially given their VERY minimal blurb regarding these changes:
"Champions with spammable targeted spells, like Pantheon and Cassiopeia, put opposing laners in an awkward position: fight back and draw minion aggro, or just take the punishment they hand out. Changing this mechanic will make those champions a lot more intuitive to play against, as well as easier to balance."
Maybe these champions will be easier to balance, but that is a LOT of champions which will probably NEED balancing, and soon.