Maybe it's just me, but when I tag someone playing a musical instrument I use the tags playing instrument + (The musical instrument here)
the same thing I do with the piano, if someone plays the piano, I use the tag playing instrument + piano
first, i've searched playing_instrument + piano and got 649 results
I've searched playing_instrument + piano -keyboard_(instrument) and got 625 results
and finally, i've searched playing_piano and got 338 results
just in case, I read the wiki, and it only says "The act of playing a piano." which makes me think that (amost) all posts with the tags playing_instrument + piano are candidates to use the tag playing_piano although I think that is redundant.
so I wonder, is playing piano really useful as an independent tag? Is there a use for this tag that I am not seeing?