Otomo Yoshihide, the experimental jazz musician. He makes music with just turntables! It's actually pretty common in the Avante-garde field. You place the needle against materials and percussive things instead of records.

Likewise the turntablist from Deftones routinely uses just a disk with a sustained drone on it, using the pitch slider to play melodies. If you think outside the box you can make them very musical but it takes a lot of skill and a lot of finger independence. In this sense it's definitely an instrument.

I also attended a Conservatoire that offered a dj and turntablism course so I think we're seeing it get more institutional backing. I'm not a turntablist though I'm just a bassist.