Rand Paul's been getting a lot of press lately, and I have to say for a GOP nominee in 2016 he fits all the requirements of a party looking to get younger and add some excitement but stay ideologically pure.
Think about it. GOP traditionally likes their nominees to be tall white males with anglo-saxon sounding last names who happen to be scions of famous families. Check on all of those factors. Currently they also like anti-establishment conspiracy theorists. You aren't going to out black helicopter Rand Paul on your best day, unless you're his father.

Speaking of him, there's a ready list of big money supporters handy to finance a bid, AND there's the additional benefit of libertarians taking over the state party in several key states.
But what about the issues? Here's where being a libertarian has its advantages. Given that single women now make up the same % of the voters as evangelical Christians, its going to be real hard for a stridently anti-choice candidate to win the Presidency. When a guy like Romney says he's against abortion but won't really do anything about it, nobody believes him. Paul however can argue that the feds interfering in this issue violates his beliefs on the role of govt regardless of his personal views and you can't accuse him of being ideologically inconsistant. Same with gay marriage.
As part of the no-taxes-for-anyone crowd he's got that issue sewn up as well. His filibuster and confrontation with Hillary Clinton during Benghazi hearings only further his stature. Lastly, on foreign policy again libertarianism is an easier sell than the dying neo-conservative philosophy of Bush-Cheney and currently practiced by McCain. After making the necessary sop to Israel, you can take the dude's word that he probably wouldn't have gotten us involved in Iraq for example.
Mind you, he'd get crushed in the general election because he's bat chit crazy but really, who stops him from getting the nomination? Had Santorum eeked out a win in Michigan he could very well have been the GOP nominee last year and he was way underfunded. Rubio is more of a VP candidate. Jeb Bush is a retread who hasn't run a campaign since 2002. Christie is too fat and will get tarred as a RINO Northeast liberal. Rick Perry came off as a buffoon last time and besides aren't we done with Texas Republicans for President at this point? The only thing I could see standing in his way is a really deep pocketed Romney-like candidate who can win a war of attrition, but aside from the aforementioned Jeb Bush I'm not sure who that would be.