This interview with Thurston explains why they've taken most of this year off :
http://www.nme.com/news/sonic-youth/57009
"there isn’t a question mark hanging over the audience any more. Like they’ve figured it out and they appreciate it.” He added: “That's totally fine and those gigs are totally fine but they’re also a bit business as usual and that kind of turns me off a little bit. So I wanted to back away from that for a while and do other work.”