The short hair is something Wasp has always sported, while Lilly tends to keep hers long so in the most superficial way possible this would suggest she could become the superheroine at some point. I think Lilly's hiring is the more convincing evidence because of her history playing tough female characters. She'd make for a natural fit on the Avengers if Marvel decided to go that route.
But there's another reason I think she'll end up as Wasp and it has everything to do with the character's history in the comics. Her relationship with Hank Pym is defined by domestic violence and is one of the most polarizing to fans, especially female readers. Just as Marvel has stayed away from Tony Stark's alcoholism in the Iron Man flicks they will likely steer clear of this storyline, too. One way of doing that is by making Hope the Wasp rather than Janet.
On that note, Badass Digest says Hope does not become Wasp in the film...yet. They seem to think she's being set up for the role, though, while acknowledging that rewrites by Adam McKay and director Peyton Reed may have changed things beyond what Edgar Wright had planned. Still, it seems unlikely that the script has changed enough that a brand new superhero the stature of Wasp would suddenly be included. On another note, Janet van Dyne may not actually be dead as Wright and Joe Cornish's script merely said that she was "gone".
My guess is Ant-Man will end with Hope getting juiced with Pym Particles and making the decision to follow in mom's footsteps. We'll find out when the film opens on July 17th 2015.
