Riven was one of the top 3 strongest toplane champions for basically 3 months now. I'm very glad that for at least 2 weeks we wont have to deal with her absurdity. Unless, of course, Riot decides to slap a hotfix buff to her, which I sincerely expect to happen any minute now, considering their history with balancing popular champions.
Obviously, her winrate will stabilize throughout the duration of the patch. I expect her to stand at a comfortable 51-52% winrate after people get used to her. This is still not ideal for such a popular champion but it's a step in the right direction.