Is 50M possible? Yep... 16M over the next 11.5 months...
Is it likely? Too early to say...
Sony seems to be gambling that having a similar motion controller to Nintendo (but better in my opinion), 3D, and Gran Turismo are going to drive sales through the holiday. If they all take off they may be able to... But, two of the three are large gambles.
On the motion controller front we haven't seen a lot of people say "I have to get a PS3 for this". PS3 supporters definately like it based on the boxing demo. And I have to admit it was really a good demo of the controller's use. On the core gamer front I think a lot of the core gamers don't use the living room as much as they use a den, dorm room, or bedroom (kids at home) for gaming. That to me is a big problem for core gamers adopting these controllers because of space.
For 3D it is "unproven" in the home. Personally, I don't like the idea of wearing special glasses to watch stuff in 3D and maybe it is just me, but I feel that 3D is becoming a marketing "gimmick" in retail and movie theatres to try and revive an industry destined to a decline rather then becoming a must have. Finally, how many people who bought flat panel TVs in the past 5 years will be able to justify to their spouses and significant others that they need to get another one now that 3D is supported? Especially, knowing that the next gen 3D won't require glasses and we will probably see another resolution jump.
Finally GT5... Enough said, it will sell and it will help PS3 sales. No doubt about it. Anyone thinking otherwise, really lacks a brain. The franchise is far too strong for anything else to happen.
But, none of this takes into account the competition. There are way too many wildcards to predict with any certainity. Other motion controllers, other bundle/repackaging/slim efforts, price drops, unannounced games, etc. Sony is in better shape overall then last year at this time, but is this last stand before the empire falls or a spring board forward to great success, no one can say for certain.