Can you or anyone you know play all 12 keys on 1 diatonic harmonica? I've heard of people doing it, but I don't know anyone personally that can.

I can play 6 keys, Which will probably be my limit. On a C harmonica I can play C,G,D,A,B and F. The other keys require way more bending and over blowing than I am capable of doing. Maybe some day, but not anytime soon.

I have never met the man personally, but Howard Levy can play a diatonic in all 12 keys with different temperments & tunings. I've watched several of his lecture videos and he's just downright amazing.

I've read about some that can do it, but don't know any personally. I think it's good to be able to play more than just one key on a harp, but not so much to be able to play all keys on one harp.
I think the guy, Tinus, that owns a site called tenhole.com plays all 12 on a C harp. He says he can't play all 12 on any other key harp.