RE: single battery possible?
yeah with the A123 ot LiFe packs I can't see a problem running one battery pack of sufficient capacity.
In fact thinking about it deeper, its probably best to run 2 x 1100mA.hr LiFe packs into the Rx and power the Ignition from a BEC as this provides true battery redundancy.
With one pack for Ignition, and one for RX theres still the chance of losing the plane if the RX battery dies.
In fact its much safer with the BEC because if the circuits are separate and the RX battery goes off line you better have an opto kill swithc in there that will kill the ignition as well. Without it your plane is going on a long flyaway.
The more its discussed , the better tha IBEC powered Ignition seems.