Yeah, it wouldnt be hard for then to add these security features. I dont know whats stopping them.

I found some apps that add this duress pin in droid-ify and f-droid. But i havent tested any yet. One is called Duress, an other is AlternativeUnlockXposed. Both seem to aim at more or less the same. But AlternativeUnlockXposed looks more interesting as it makes the duress pin unlock the screen and it silently runs a preconfigured command to erase something.