I'm curious to see what this ship will be as well. I seem to recall Zach saying something along the lines of them making some available outside the convention as well, as they expect it to be so popular. With that said, there's two categories for me:
Slight variant:
Last year's battle damaged Excelsior would fall into this category.
Proper variant:
I'd list the 2013 'cloaked' BoP under this category, as it's a bit more than adding some heavy dirt wash to an already existing product.
My guesses for both would be:
Slight:
1 - Battle damaged 'Generations' 1701-D. Lots of dirt wash, phaser and photon burns, and new sound clips - maybe even one featuring Data saying, "Ooooh shit!"
2 - Battle damaged 'Undiscovered Country' 1701-A. As above, but with Kirk's final log entry as a bonus sound clip (for example).
3 - Darkly-painted, rusted up 'Rotarran' Klingon Bird of Prey. Nothing too different, except the voice clips. This one is highly unlikely, but as they have the ship already made, it's really the only variant I could think that hasn't already been made.
Proper:
1 - USS Defiant NCC 1764 - made from glow-in-the-dark plastic.
2 - Add in however many name variants there are to existing ships here (Excelsior Refit named Lakota, for example).
They're the only ones I can think of as being 'likely', and if I had to put money on one, I'd go with the Defiant. That would also fit the bill as being highly sought after, to the degree where they'd make a small quantity to be put on general sale outside the con (as Zach said).