It would seem to me that Flexen's extremely poor strikeout numbers are more likely than not an omen of a quick decline in performance. I'm all for trading Kepler, but assuming this guy is then by default given a rotation spot over Ober, Varland or SWR, count me out.
If they'd plan on putting him in the pen, then, sure, I guess they can give it a shot, though I suspect trading Kepler for a middle reliever would probably draw heavy criticism from many corners.