Duuuude that's genius.

that would just ruin the whole WARFRAME thingy

Oni !!!
i want it ingame

That's a fun idea, but I'm afraid that I'm pretty sure DE keep away from things like that. They don't want anything too much like facial features, such as eyes, ears, nose, teeth, etc to be a part of any warframe helmets. I'm pretty sure this is because they want it to be clear these are beings within the suits, and the suits themselves aren't exactly normal or even human.

some oni mask ♥♥♥♥ would work for rev so well

+1

I don't know about you but for me the oni teeth are already there. You see the two spikes at the bottom of the helmet in the front view? Those look almost exactly like oni teeth.