What I would like to see is the Tie Aggressor from SWG for his back turret, which would be the first time we see it on a fighter ship.
What would be even better is an Imperial ship with a 360 turret, since as of right now, rebels have three kind of ship that can have a 360 turret vs zero for the Empire. They need some love too.
Other than that, YT-2400 would be cool since I like the design; but it's more the collector talking than the player, since I don't really see what it can bring to the table that the YT-1300 can't already... Other than a fourth rebel ship with a 360 turret...
Like a lot of people, I would like to eventually see clone wars ship, but for a seperate game. I hated the prequels, but really liked the cartoon, so I made peace with the clone wars era.
Speaking of cartoon, Star Wars Rebel start to air next fall I think, so maybe we'll get a wave 5 preview there before the new trilogy start.