I think at least one of them is going to force their way up at some point if Peguero, who has an option, keeps melting down with runners on base. I don't know how you feel comfortable pitching him in anything but the lowest leverage situations in the postseason, if at all. Milner still has to earn back his spot on the roster and his continued fit is questionable given the presence of Ashby, Koenig, and (hopefully) Hudson. And let's face it, a reliever or two is still likely to hit the IL at some point this month.
Like you said, the Brewers remain committed to developing Misiorowski as a starter which means he's all but guaranteed to open in the minors next season. So, they'll likely retain the extra year of control regardless.
Yoho is turning 25 and has had two TJ surgeries. I don't see much of an incentive to holding him in the minors much longer. Devin is going to be gone at some point within the next several months, and I think Yoho has a real chance to make the team out of ST.
Not too worried about 40 man spots given guys like Herget and Jay remain on the roster.
Bottom line is there's a major opportunity to capitalize on yet another "bite of the apple" and Misiorowski and Yoho's stuff is as postseason caliber as it gets for two guys on the major league doorstep.