There are currently 19 ships that have been released for X-Wing that have not made their way to Armada:
Scum Y-Wing
Scum Z-95
M3-A Scyk
Starviper
K-Wing
TIE Punisher
Kihraxz
Inquisitor's TIE
MIst Hunter
T-70 X-Wing
TIE FO
ARC-170
TIE SF
Protectorate Fighter
Sabine's TIE
U-Wing
Upsilon Shuttle
TIE Stalker
Quad Jumper
Not likely:
Scum Y-Wing, Scum Z-95, Sabine's TIE
We're nowhere near the point where we need to see cross faction fighters. If they ever release a Scum Faction, we might see the scum versions, Just don't hold your breath.
Possible (Scum):
M3-A Scyk, Starviper, Kihraxz, Mist Hunter, Protectorate Fighter, Quad-Jumper
These would fit best in a Scum faction, but we might see them flying with rebels. The empire has way to many TIE variants to need most of this Scum.
Possible (TFA):
T-70 X-Wing, TIE FO, TIE SF, Upsilon Shuttle
These look way to close to existing fighters to warrant new models, The Upsilon being the exception. Even it could be represented by new cards with TFA artwork.
Most Likely:
K-Wing, TIE Punisher, Inquisitor's TIE, ARC-170, U-Wing, TIE Stalker
It's and eclectic bunch, but they all have a distinct look.