There was talk that the Rangers were seeing how much interest there was in Harden and Feldman today, and I'm assuming there wasn't much. As I've indicated before, I don't think the Rangers are interested in just dumping Feldman and his salary, and Harden is probably going to have to show something to garner interest.
My guess at this point is that the Rangers figure they know what Feldman is, and don't see him as a member of the playoff rotation. Harden is different, though...I suspect they want to give Harden 2-3 starts to show them that he's back and track and is the guy they thought they signed. If he can do that, he sticks in the rotation the rest of the year, and is probably in the playoff rotation.
And if not, if Harden is the guy we saw earlier in the season, then the Rangers will probably just go ahead and cut him loose.