Ninjas should never get unmasked.
They loose the mysterious assasin stuff, and they look cooler with masks. The reason I always hated MK3 was the lack of ninjas and unmasked Sub-Zero who ill never recognize as Sub-Zero.
I totally agree with you, BUT I think it's interesting to see just for curiosity, specially if it's just under broken masks. But no, I'd never like to have every ninja with an alternate unmasked costume.