I do see Rubio's strength as a candidate, but I'm not convinced that the boost he's been getting recently will stick. Rubio's been fashionable twice before in this primary season, and he faded both times.
The GOP Establishment has no real alternative to Trump. Rubio has shown some staying power and resiliency. Everyone else hasn't caught on, and I believe that the "No More Bushes" message is being received loud and clear.
It remains to be seen if Carly Fiorina has staying power. She's not really an "outsider", and she's the one "outsider" that the Establishment would be the most likely to make an accommodation with, but only for the VP level. This would all hinge, of course, on whether or not she shows some staying power; the attacks will be coming in three . . . two . . . one . . .
Right now, I think the GOP Establishment would like a Rubio-Fiorina ticket if they could make it work.