I think a Kasich/Rubio ticket could compete in PA, but it would be tough.
I actually still think Trump won't be the nominee.  Come vote time when people close the curtain, I think the "poles" aren't really as accurate as some think.
As more of the low-level guys drop out, those votes for traditional candidates will start to coalesce.
Rubio is starting to make hay.  And despite my worries I still think Cruz has a good shot.  As Bush, Huckabee, Fiorina, Christie and Paul drop out, I think it tightens up to a 25%-25%-25%-25% battle between Trump - Carson - Rubio - Cruz.  I wish Kasich would be in that mix, but I don't see it but he's getting my vote regardless.
Carson is really hitting home with the religious right.  Not sure why, but his soft, pious voice is working.  I thought he'd have faded away by now, but he's not.
But as this field drops to 4 or 5, it really gets interesting.  I've never seen a primary this close among that many candidates before.