Rubio seems to be on a very good trajectory. He's going to shine at every debate - only Fiorina, Christie, and Cruz come close and even they aren't really in the same league. More importantly, he's doing decent with fundraising and is just now starting to build his ground game in the early primary states.
The more dead wood that gets cleared from the field, the stronger Rubio is going to burn. Jeb! folding in the next few months would be a bonanza for Rubio in terms of donor support. Still not sure that's going to happen, but there are reportedly rumblings that Jeb! is on the verge of risking donor defections due to his anemic polling.