Warpath and Sunspot were
both New Mutants, so technically we had two.
True.

ETA: Was Siryn ever with the NM, or did she come in after the name-change? She was in X2 (another continuity issue-- How does Sean Cassidy have a teen daughter in the early '00s if he was killed in the 60's?)
Speaking of Sunspot and Warpath, Fox has already announced that they're developing an X-Force film, so I wonder if those two were included in DoFP as a sort of soft tie-in to that future movie.
That would be very cool. And I imagine that "X-Force" is a more marketable name than "New Mutants", anyway.
I think Cannonball and Wolfsbane would both work on screen as well, but Karma and Moonstar's powers are probably too similar (in that they are both psionic based), so one of them (at least) would get the ax.
Magik's origin would make an interesting movie. Magma has a unique power-set that would be cool to see visualized. Boom-Boom? Rusty? Skids? Cypher (for bullet bait?)?