based on the news conferences and McD interview on WGR, to me it sounds like he is set on going with Peterman for the rest of the year, just my opinion
he probably knows that the writing is on the wall for the defense, not enough talent, not getting the lucky bounces anymore and he wants to evaluate Peterman to have all the information he needs before the 2018 draft
I think Beane and McD were planning on this being a rebuilding year all along and they probably surprised themselves in the first half, now he probably knows the writing is on the wall for the talent level on the team (especially defense).