A manager at the Production Central store at Citywalk confirmed it'll be Firehouse Subs. Higher up than the Dippin' Dots guy, but a more credible source. Admittedly unverified, of course. But it does make a lot of sense. Regional chains seem to be the rage lately (The Habit, Pinks, and VooDoo leading the charge), and I'm okay with that over a national chain I can get literally anywhere else.
I don't know if they really could put a Raising Caine's in the old Ludo Bird space. It likely is way too small, and my own wishful thinking. But if they can make it happen, I bet it would have lines that would rival VooDoo.
On a side note, anyone know why Panda at Citywalk hasn't opened? Is that possibly going away as well? Again, total speculation, but it wouldn't surprise me. Extended closures seem to be an ominous sign. Same with the Poke place.