Could be Delta, or could be Alaska. Virgin America's about to lose their current gate area, so I could see the future Alaska consolidating over there.
I believe that JetBlue has more input on their gate areas (and more direct investment) than the other airlines do. It's uneven that way. United paid a lot for their gate expansion, which is why American couldn't be consolidated by shifting United a few gates down. It doesn't seem like AA is paying anything for this, though, and certainly Southwest isn't paying for any of their moves.
I think the C piers will get renovated on JetBlue's schedule, not Massport's.