Barta was interviewed by The Daily Iowan within the last two weeks (so I didn't bother to find the link), and he was asked about alcohol sales in Kinnick and Carver. His reply was the same as it has been recently. To paraphrase: Iowa won't be the last to do it; it's coming, but I don't know when. And when it does come it won't be for the money; it will be because we want to accommodate the best fan experience. [end paraphrase]
The pressure is building, so I think the 2020 guess is probably not far off. I don't think they can wait much longer than that. And I say that as a nondrinker, but it just makes sense. Prohibition in college sports facilities is ending, and I don't think crowd behavior will change one iota. It might even improve because people won't need to get most of their drinking in before the game.