This seemed very familiar to me. I remembered seeing Square offering a POS kit[0] just this spring. Interestingly though, they no longer sell it and instead are only offering a (very slick) stand/reader[1].
I wonder why they stopped offering the whole kit. My only guess it was a MVP style trial balloon offering to gauge interest before building their own hardware. Or, it didn't fly, which may not bode well for Shopify either.
[0] http://appleinsider.com/articles/13/02/20/square-launches-ip...