There really are 2 frontrunner imo for the next imperial ship.
Scimitar Assault Bombers and the Assault Gunboat.
The Scimitar does step on the Tie Bombers toes a bit, they would have similar stats but would likely be more bomb focused w/ 2-3 bomb slots and less projectile slots.
The assault gunboat would also have similar stats to the tie bomber except less hull and more shields. The gunboat would be a cannon platform and maybe have 1 torpedo slot.
Based on what Alex says, I would say the scimitar assault bomber is more likely.
(The missile boat is an outlying possibility but I have a hard time seeing how it would be any different from the tie bomber when translated in game)
Not counting obscure video game sources, Rebels only have 1 ship left that makes sense and that is the Kwing and it seems like it would make sense here.
Again, the Otana is an outlying possibility but I have a hard time differentiating it from the other 2 YTs.
I'd like to see the skipray blastboat but I agree it needs a new base size. (It would need a wierd 1x2 base).
Not too familiar will possible scum ships to speculate.