I understand that it strikes some people as ridiculous that people are engaged in early 2016 primary speculation already, but I think it's important to understand that this is a very legitimate nonfrivolous undertaking. If you want to understand politics and public policy in 2013 or 2014, you have to understand the 2016 race.
For the record, I offer hearty thumbs up to my colleague David Weigel's skepticism that Elizabeth Warren actually does pose a major threat to Hillary Clinton's aspirations. That said, it does seem to me that a Warren-beats-Hillary scenario is a lot more plausible than a Cuomo-beats-Hillary scenario or anything else you could sketch out there. Which is to say that if Team Hillary is going to spend time worrying about anyone, then they'd do well to spend their time worrying about Warren. As party professionals are already working on the Clinton campaign, it's by no means "too early" to think that things prominent Democrats say or do are influenced in part by their thinking about 2016. The basic dynamic where Clinton wants to be president, where anti-Clinton populist elements see Warren as their most plausible anti-Clinton vehicle, and where members of Conrgess think about these facts as they consider policy issues is a real thing. You saw in the failure of the Larry Summers for Fed trial balloon that there are meaningful gaps between Democratic Party legislators around these issues, and the nomination context will start to feed into those substantive disagreements and vice versa.
Conversely, on the Republican side now that Chris Christie has triumphed in his re-election campaign, the 2016 nominating campaign is a key factor in substantive policymaking in the state of New Jersey. The same is probably true of Texas, Wisconsin, and any other states whose governors are eying a run. You can roll your eyes at it if you like, but it's certainly not too early for these governors to be thinking about how their actions will impact their prospects—and that means it's not too early for citizens to care about what's happening either.
What people shouldn't do is offer dumb speculation. The single best guide to how to think about these contests, in my opinion, is The Party Decides. If you want an informed guide about how to speculate, I'd start there.