Well 2013 turnout would be better than 2014 turnout but I think 2014 turnout will certainly be better than the 2012 turnout.
I question whether Warren could have won in a midterm (unless it was an anti-GOP year).
In a midterm against an incumbent Senator Brown, maybe not, but she’d be the favorite in an open-seat race just because if the D next to her name and her certain fundraising advantage (Brown wouldn’t have raised as much as a challenger—2011 was an aberration created by people thinking that the Dems needed a 60th vote for Obamacare instead of just railroading the House and using reconciliation to tie up loose ends).