I've gone with the NES. Simply because so many people these days go out and buy consoles I don't think hitting 60 million over the space of what....the next 6 or 7 years is that far fetched, even if its deemed somewhat a failure by that time.
You'd imagine it will easily clear 10 million by the end of 2014. If you think it will have a shelf life of at least 6 more years it should comfortably pass that mark by then.
PREDICTIONS FOR END OF 2015: (Made Jan 1st 2015)
PS4 - 34M - XB1 - 21m - WII U -12M