Sabato moved 13 House seats towards the Democrats, only one towards the GOP
Here's his article outlining how a Dem takeover might happen
http://www.centerforpolitics.org/crystalball/articles/house-2016-how-a-democratic-wave-could-happen/
Basically if you took Obama's vote margin from 2012 and give him three extra points, that's enough for him to go from winning 211 districts to 241 - in 2008 (under current district lines) he won in 242. Obviously ticket splitting is still a thing and the change wouldn't be applied universally so that would be no guarantee that this would result in Dems winning 241 seats, but the GOP would then have 56 districts that voted one way for the presidency and another for Congress. If the Democrats picked up barely over half of those they'd win.
I really think if Trump or Cruz were the nominee and as disastrous as everyone is predicting, that could do the trick. The problem with gerrymandering is that if you spread your GOP voters too thin, a wave could make a bunch of incumbents vulnerable who shouldn't be. It just takes three extra points for Democrats to flip 30 seats. This is exactly what happened in 2006, where GOP gerrymanders fell flat in places like Pennsylvania because those R+5 districts suddenly weren't so safe in a D+8 year. As Sabato points out, all but two of the 30 seats that would flip to Obama are in blue states.
I still wouldn't put money on it, but we already have polling suggesting 2016 will be similar to 2008, which could be good news for John McCain or something. I totally believe that Ted Cruz compared to Romney, along with demographic shifts since 2012 could turn Obama's 4 point victory into a 7 point win for Clinton.