I think we tend to underrate Biden's odds of being the 2016 nominee. If (in advance) it seems likely that the election will be a bad one for Democrats, he's probably the single most likely nominee. (In any other situation, I'd completely discount him.)
I agree and there's two fairly plausible scenarios. Obama's re-elected and there's another downturn by early 2015. Or Romney wins this year and the recovery picks up a lot of steam. Probably would be a lost cause but also Biden's last chance and for whatever reason, he seems more interested in trying a very uphill race than Hillary would be if it came down to it.