You don't have to like it. I predict now it will be Clinton-Castro.
Bookmark this for future soothsaying. It is early. You can chastise me for predicting early. We got 2014 to focus on. All well and good, I am making this prediction now because I want to call it early.
Clinton cannot shore up liberals and it risks causing a rift between liberals, and centrists and third wayers (DINOS). The problem is with the independent vote. Clinton can get the independent vote fairly easily and a lot of the conservative women vote (if only voting because they identify with Clinton). However, the independent vote requires liberal activists to GOTV and rile up the base, as liberals have always done.
To satisfy the liberal vote Clinton needs a true liberal on the ticket. Castro shores up the Latino vote, again for identifying purposes, but it doesn't go far enough to cause a massive GOTV effort. In Latino communities that will be the case, but in more conservative communities the liberal GOTV effort will be paramount. And for that reason Clinton will need someone more progressive on the ticket.
Castro will accept because he suspects by 2024 he will be a shoe in for President as the Latino community will have grown to be 15-20% of the population. And his progressivism will be accepted in 2016 and 2024 the country will have shifted dramatically to the left (by then marijuana and gay marriage will be legalized across the country; and the American public will be wanting Single Payer which is what his platform will run on).
Some will say Clinton wouldn't need Castro or that Castro wouldn't jump on board a Clinton ticket because she is too centrist / right wing / third way. I think that Castro would be on the ticket because he wants to change America and being VP and then President is his best shot at that. The demographics of the United States are statistically going one way.
If climate change doesn't screw us in the intrim this is how I see the future panning out.
Chastise away. 
edit: TBF first posed this situation though I don't think she outright predicted it (she did make convincing arguments for this, however). Credit goes to TBF for convincing me on this issue though I am fully compelled to believe this will be the candidacy. It's been in the back of my mind for weeks now and I finally committed to making a prediction this early.
= new reply since forum marked as read
I will defend you if anyone trashes you for calling it early.
Glad you agree if Clinton runs she'll need a progressive on the ticket. I was afraid someone would call me out for suggesting that (most of my post pushed the ticket needing a progressive).
The individual I'm thinking I'm all but convinced will be a very, very strong contender for the number two spot, therefor I'd like to refrain from giving trolls a preemptive political target.
Have a great weekend, my friend! 
.. unfortunately I also predicted the 'thugs would use the 'Castro' name as a wedge.
How ever I do think it will happen!
Now, can we have Warren for Atty. General 
?
and he went to better schools.
It's no contest.
...as he's only the mayor of a city not considered a "major" city (like NY, Chi., LA), he would be labeled unqualified. Yes, I know, the Palin makes any "unqualified" argument moot in perpetuity; nevertheless, that's what the media and the right will pound-pound-pound daily. It might not matter, because the support from the Latin community would be enormous and might blow all of that out of the water. It would be risky, but I do like him a lot. If only he were a congressman... like his brother, elected only last year, though. But I think Julian has more charisma than Joaquin, and would be the better pick as far as that goes. If only he were a governor.
You never know, you might get your wish.
Remember at the convention when his little daughter saw herself up on the big screen and started preening? Adorable!
I imagine it's going to be tempting for Hillary to go that way. In spite of the qualified issue for Julian, she'd have women and the Latino vote locked up, as well as African-Americans and other minority communities, and the youth vote. I don't think his status would really hurt in the long run. An argument could be made that she's qualified enough for the both of them, LOL. As long as he's scandal-free, it's hard to see how that ticket would lose to anyone the GOP can muster.
I think I just talked myself out of my own argument.
Edit to add: just saw your post above about Christie/Martinez. That would make it very interesting. 
