And even if he was touring or playing shows, a big part of the musical guests playing at Kumoricon is them being requested or asked to play by the people at KUmoricon. For example, A-Key Kyo have played at Kumoricon for at least two years, and even though they really wanted to play again this year, no spot was extended to them from Kumoricon officials, so they aren't playing. That's what I think is going on anyway.
But, I digress, yeah, hopefully we can see Piano Squall come back some year.