The strategy for both parties, for most elections, has been to balance the ticket with representatives of the different wings or the party. Sometimes this gets talked about as "regional balance," but that just obscures the fact that regional differences have tended to be ideological. Eisenhower/Nixon, JFK/LBJ, Nixon/Lodge, Nixon/Agnew, Carter/Mondale, Reagan/Bush, Bush/Quayle, Dukakis/Bentsen, Dole/Kemp, Bush/Cheney, and Kerry/Edwards were all tickets that attempted to unite distinct wings of their parties; they all also happened to achieve regional balance. That's been the norm.
There have been the occasional tickets of two candidates from the same wing of the party -- Goldwater/Miller, Johnson/Humphrey, Humphrey/Muskie, McGovern/Shriver, Clinton/Gore, Romney/Ryan -- but all of those except Clinton/Gore still achieved regional balance.
(I wll confess that, to this day, I don't know how to explain Gore's WTF choice of Lieberman, but even that was a regionally balanced ticket.)
So I do think Metric is right: a ticket of two ideologically-similar candidates from the same region is not the norm. I'd add again that the fact that it worked once, with Clinton/Gore, had much to do with the fact that they were both from a region where the Democratic Party was in trouble, and where they could help shore up its weakening strength while taking solidly Democratic states for granted. That dynamic would not be present in a Sanders/Warren ticket.
In all, though, I'm with you: I want Warren in the Senate, where she'd do far more good than as Veep; and I think Hillary is far more vulnerable in a general election than is often acknowledged, so we need to have a strong bench for 2020 just in case (and luckily, I think we do, including not only Warren but also Sherrod Brown, Tim Kaine, and Kirsten Gillibrand, all of whom I wish were running this year instead of HRC).