Is there any reason to believe they're going with two Ant-Men, rather than Hank Pym with something of O'Grady's personality?
At least twice in separate interviews over the course of the films development (which no doubt will continue to evolve a bit more) those involved have dangled the prospect of either a Pym/Lang co-existence in the film or Pym/O'Grady.
dateline July 2011
Cornish says something about the script with Multiple Ant-Men:
"As for whether or not the movie itself is moving forward remains up in the air. “I don’t know, man. I’d love for it to happen but it’s really up to Edgar and Marvel,” Cornish said. We had heard that at one point Cornish and Wright were going to put several of the Ant-Men (meaning people that had put on superhero scientist Hank Pym’s suit) into the script, meaning that they could have thrown in our personal favorite Ant-Man – Eric O’Grady, low-level S.H.I.E.L.D. Agent turned shadily “Irredeemable” Ant Man.
dateline June 2012
Edgar Wright revealed some details about the planned plot of the movie:
"'The idea that we have for the adaptation is to actually involve both... Henry Pym and Scott Lang. So you actually do a prologue where you see Pym as Ant-Man in action in the 60's, in sort of 'Tales to Astonish' mode basically, and then the contemporary, sort of flash-forward, is Scott Lang's story, and how he comes to acquire the suit, how he crosses paths with Henry Pym, and then, in an interesting sort of Machiavellian way, teams up with him. "
Now if they go with the Pym/Lang duo that frees up casting to make an older Pym AND have a type of period piece film (for portions of the film) that could maybe tie into Captain America and Winter Soldier...if necessary. Not sure fans would want a 60yr old Pym though. Kinda takes Wasp out of play as well.
Even still, could just be a solo Pym movie. Leave the sequels for expanding to Lang and O'Grady. It could be the first film series to have actively evolving leads...on purpose. That would be a first would it not?