Now it is pretty obvious that the missing SKU is a wave 13 tie in ship to The Last Jedi. It is something that The Mouse doesn't want to discuss openly right now, so FFG is not allowed to announce it. Seeing that there already are Resistance and First Order ships coming in wave 13, it would make sense that the missing SKU is a Scum ship. I think the most likely candidate is DJ's ship (Benicio Del Toro's character). But....
This movie seems like such an obvious place to bring in new content for the most famous character in Star Wars, namely Luke. There are rumors that Luke's old T-65 X-Wing is hidden on the seabed near his island. I think people would go nuts seeing Luke in his old T-65, and Disney must know that. Episode 7 was all about the original trilogy nostalgia, and this seems like such a good opportunity for more of it. So could the missing SKU be Luke in a T-65? It would make sense that Disney would want to keep this kind of key plot point secret until the movie comes out.
There is also a lot of ambiguity in Disney's marketing whether Luke is really still on the light side at all. Could he be no longer aligned with either faction and have his own agenda? Could that mean Scum Luke in a Scum T-65? Obviously this would include the long demanded T-65 fix as well, and with the recent FAQ and Gunboat on the way it appears FFG has taken a renewed interest in trying to deliver exactly what their players are begging for.

