Intriguing idea indeed, even if it isn't quite new-- the Nano name has been floating around for a while. There are four other products sliding out of the rumor mill as well-- AppleTV is rumored to get an update (and a hard drive), and supposedly we'll see a MacBook Nano as well, the long-rumored ultraportable that Apple is supposedly working on-- a.k.a. Rumor #3.
The future of Mac, or wishful thinking? At this point, we have no indication-- Mac OS Rumors is no 9-to-5 Mac (ouch, but they deserve it, don't they?), but they are called "Rumors" for a reason. Either way, I want to buy an extremely small, compact, headless Mac with Leopard on it this fall. Whether it's called mini or Nano doesn't matter to me at all.