As a preface, I think the observation made in a few places about a change of release pacing by FFG seems likely. With three factions out there, reducing new waves from 4 to 3 ships just seems to make sense. It gives players a breather in purchasing to buy more FFG products (catching up on all the many waves of X-Wing releases for new players, buying into the new 'Imperial Assault' or 'Armada' games, starting to buy into the 'Epic'-scale X-Wing game, etc), it slows down the need to dig into the EU for more content to use, reduces the amount of new 'X-Wing' content to playtest...
3-ship waves from this point on just makes sense. So my predictions will be for three entries...one from each faction.
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Imperial: TIE (Scimitar-class) Assault Bomber

Reason: Alex Davy's quote that 'if you like the TIE Bomber, you'll love wave 7'. And what is the TIE Assault Bomber but the B-Wing to the TIE Bomber's Y-Wing? Combined with the comment that wave 7 would include some new options for bombs/ordnance...well, you need a bomber, don't you?
Expectation: Take the TIE Bomber, reduce agility, add hull and shields, add expansion slots, increase price. TIE Assault Bomber is the Y-Wing -> B-Wing progression, with the TIE Bomber as Y-Wing, basically.
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Scum: YT-2000 (Otana)

Reason: FFG's recent preview art (right above). FFG has fairly consistently commissioned art projects in batches, and often re-used ships or characters across games. So the RPG release above is...telling. Moreover, the Rebels have a primary-360-turret ship, the Empire has a primary-360-turret ship...the Scum faction does not. The only named YT-2000 we have is the Otana, which was flown by Ace Azzameen...oh, yeah, the guy whose brother is already in the Scum faction. And he never flew the Otana on 'Rebel' missions, just third-faction (sorry, "independent") missions, so...
Expectation: Nothing really special, here. Probably a mix of the YT-1300 and YT-2400 (arguably fitting, given its model number). Say, the upgrade slots of the YT-2400 with the YT-1300's dial, and no particularly unusual title?
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Rebels: Uhhhhhh...K-Wing?

Reason: Okay, I'm really reaching here, but the number of 'obvious' Rebel releases is getting pretty thin. Given a reference to wave 7 as a wave that fixes/improves ordnance, we'll want at least one more heavy-ordnance carrier to get more upgrade cards in the mix. Yeah, I've picked the Lego proposal of it, as, honestly, that's the least HIDEOUS version of the craft I've seen, and most 'consistent with Star Ware lore'. Sure, it breaks pretty hard from a lot of the EU material, but, heck, FFG created the 'Imperial Raider' whole-cloth, tweaked the Z-95 to borderline non-recognition, and even modified the TIE Defender from some of its representations. Sooooo...if they pick up this guy, I'm assuming they'll "fix" it.
Expectation: If you were to type fighters into 'swarm', 'superiority', and 'assault' - with the Z-95, X-Wing, and Y-Wing being the Rebel's first pass at those ideas...the K-Wing would be the 'assault' fighter to the E-Wing's 'superiority' fighter. IE., expensive, but arguably worth it. (And really pushing the boundary between 'small base' and 'large base' craft in a way that even the B-Wing/E2 doesn't quite manage, yet)
