Does this take the decision out of Edgar Wright's hands about casting for the Ant-Man movie? Was he involved and agreed to Nathan? Ant-Man is on the list still as one of Marvels likely sub-$50m movies. Seems an Ant-Man movie has a better chance as a solo film post-Avengers unlike the other Avenger founders who are all getting a solo first.
Come to think of it, didn't Wright, when asked which of the various Ant-Men the comics have offered up he'd use for his movie, say he intended to have a couple of them in the film, playing on the legacy aspect? If so, he could still get his own actor for the Ant-Man (or Ant-Men) who he wishes to focus on (a comedy is better suited to an Eric O'Grady than it is to a Hank Pym anyway), with Fillion's Pym in a supporting role.
Fictitiously yours, Trent Roman