http://www.usatoday.com/story/sports/ncaaf/big12/2016/05/02/big-12-expansion-membership-title-championship-game-new-schools/83853258/
That doesn't sound like very much, but the question is whether the likelihood increase is relative or absolute. Let me explain. For simplicity's sake, let's assume each P5 conference has an equally likely chance of making the playoff (I know it isn't reality, but just roll with it here), which is 20%
Relative Increase of 5%: 20% * 1.05 = 21%
Absolute Increase of 5%: 20% + 5% = 25%
My guess is that Bowlsby was talking about an absolute increase, and that makes it a much more compelling case for adopting a 12 team, 8 game football conference schedule.