No, at least not yet. There was a Toronto Sun interview with the director, Peyton Reed:
[K]eep a very sharp eye out when Ant-Man enters the quantum realm. “I would say just watch out for something, maybe in the corner of the frame, something you might see also reflected in Ant-Man’s helmet,” said Reed. “By the time the DVD and Blu-ray come out and you can single-frame it, it’s there.”
That's as specific as I've seen him get. Other outlets have interviews that contain variations on this theme, he merely confirms that the reflection is a purposeful Easter Egg, but does not discuss what it's a reflection of.
In a Comic Book Resources interview, Michael Douglas mentions what he'd hope a future film to delve into:
I think in this one I had to carry a lot of plot and exposition. In the next one, I hope things get a little more bizarre… the Quantum Realm!
But since that future film hasn't been written yet, it's just guesswork at this point.
However, Kevin Feige did tell The Hollywood Reporter that the Quantum Realm links not just to the hypothetical Ant-Man 2: Too Many Ants-Man, but to things in Phase 3:
How does Ant-Man fit into what you call the Phase Three cycle of Marvel movies?
FEIGE It really is the movie that closes out Phase Two. Phase One ended with Avengers. So some people thought that Phase Two would end with an Avengers film. But the truth is, there is so much in Ant-Man: introducing a new hero, introducing a very important part of technology in the Marvel universe, the Pym particles. Ant-Man getting on the Avengers' radar in this film and even – this is the weirdest part, you shouldn't really talk about it because it won't be apparent for years – but the whole notion of the quantum realm and the whole notion of going to places that are so out there, they are almost mind-bendingly hard to fathom. It all plays into Phase Three. It became very clear that Ant-Man is the pinnacle and finale of Phase Two and Captain America: Civil War [May 6] is the start of Phase Three.
And back in March 2014, Feige told Birth Movies Death:
Are you watching the Cosmos series? That’s magic, [the quantum physics]. It’s unbelievable. If somebody knew how to tap into that stuff, what’s the difference between that and magic?
You don’t get into it in Harry Potter, but if a scientist went to Hogwarts he’d find out how some of that stuff is happening! We’re not going to spend a lot of time on that, but there will be some of that. And particularly for a character like Strange, who goes from a man of science to a man of faith and who traverses both worlds. And sometimes there won’t be an answer! Sometimes he’ll want an answer - “How is this happening?!” - and nothing.
This suggests that we may see the Quantum Realm again earlier than Ant-Man 2, in 2016's Doctor Strange. This provides some fuel for the idea that it could be a cosmic entity's silhouette.