The only problem with Rubio is he will not get the Hispanic vote. The Republican Cubans have made it their business to distance themselves from other Hispanics in the past and in a national election he would surely fail due to getting only the Cuban and white Republican vote, which will not be enough to put them over the top.
Rubio definitely won the non-Cuban Hispanic vote in Florida in his 2010 Senate race. Now, whether that'll translate to a federal election, I don't know (and frankly I doubt it), but Rubio doesn't have to win the Hispanic vote -- he just has to do very well. Against, say, O'Malley or Cuomo -- somebody who doesn't appeal to Appalachia -- if Rubio can get into the low 40s in terms of Hispanic vote nationwide he should be able to win. Of course, if AR or KY or WV and like states are in serious doubt there's probably no way Rubio can make up for that with Hispanic votes.
