I see another Imperial Aces including the Defender - background wise all pilots had to be aces to get into the thing, in the Tie Fighter game you fight along-side Darth Vader on several missions, so a Vader pilot card for the T/D makes sense... perhaps a Title for it. Might make it pricey as can be... so might not be a popular choice but makes sense... or a Tie Fighter aces pack.
Perhaps an X-wing/Y-wing repaint Rebel aces with some nice titles or upgrade set (lots of un-love for Y-Wings, maybe a title or mod could make them popular again)
If they do another set of Aces for each side I'd imagine a lot of stuff for balancing effectiveness of ships so we might see much more variety in tournaments.
Transports the size of the falcon that have appearances in games/films/etc seem a good bet, Outrider probably guaranteed.
If they do Nebulon B frigates then maybe a Nebulon B for the rebels as the medical frigate and a Nebulon B 2 for the imperials so there's an option to have different models for both sides - but it's a big difference in size between a CR90 and a NebB (300m vs 150m... might be too big and expensive).
Imp Assault gunboat would be a logical choice (though maybe very close to a B-Wing statwise, which might make it less likely... FF seem to want fleets to be different between the two factions).
Rogue squadron X-wings would be really nice touch, but I wonder if there's a copyright issue...
And if they did 12 alternate paint X-wings the Imperial player would be crying out for something similar - even if they had to make stuff up for it - Imperial navy was much grey'er but I'd imagine they could come up with something (Royal guard Tie Fight and Defender maybe? Or perhaps some variation based on new republic)