You said they were worried. So they're not anymore? I wonder what they came up with to balance the skirmish trait? Maybe creatures with the skirmish trait might take recoil damage? Or better yet, they might only be able to attack before they move and not the other way around? Or maybe they have lower life or less attack dice so it takes less attacks to destroy them then they can dish out. They're probably still hindered when they try to leave the zone, after all, and I'm sure they're still vulnerable to ranged attacks too. I would imagine it might be difficult to land full action melee attacks on them, but that seems good and thematic IMO.
Yeah, I doubt they're still worried. If I can think of all that on the spot, then they probably thought of all of that and more months ago, and playtested it too. I can't wait to see it!