Aren't they already running in a push/pull configuration?
BL is a private company so they needed to work out the economics of this to justify its existence. Something about going to true high speed put them in a situation where it wasn't financially feasible for them. At least not for now. Rumor is BL west (Vegas to LA) might actually be feasible. My guess is because of R/W cost. The land out in the desert is probably cheaper than developable land in Florida.
Actually looking at their site, BL west looks to be using different trainsets altogether, so it might very well be limitations on the rolling stock.