Unplayable Music!

[squidgelet10]

Greetings each.
I often hear presenters, particularly on my favourite radio station <ClassicFM 100-102Mhz>, referring to a piece of classical music which was branded as UNPLAYABLE at the time it was written (e.g. Tchaikowksy Piano Concerto/Sibelius Violin Concerto etc.).
Does anyone know of a piece of music, classical or otherwise, which is STILL technically unplayable by conventional means?
Cheers!!

[willa]

I don't know about unplayable, but my violin teacher roundly curses R. Strauss for the opening passage of the Don Juan Overture. :->

[brachiopod]

A few of John Cage's pieces, perhaps?