I'll start by saying of course the listing was quickly taken down. Don't look at me if you can't find it after reading this. Now, that said, let's get to it.
It would seem a listing for a new Metal Gear game, apparently titled Metal Gear Solid V: Definite Ex, briefly appeared on internet retailer Amazon. The listing was, also of course, quickly posted to Reddit and once it began to steamroll on, the listing was taken down. No such announcement has come from Konami, so this obviously looks like a mistaken listing.
Still, with a subtitle like "Definite Ex" the most obvious speculation is that it is likely a definitive edition, including Metal Gear Solid V: The Phantom Pain and Ground Zeroes together. It remains to be seen if Konami will announce any such title, as they seem to be going all in on those pachinko machines they love.
Konami hasn't lately garnered much goodwill from their fans, so it would be interesting to see something like this released. I would very much like to see how something like this sells after all those disappointing pachinko machine announcements, as well as Kojima leaving the compant and the cancellation of Silent Hills. Yea, gamer goodwill is likely at a very lowpoint right now. Perhaps they hope this could turn that around? I doubt it but its better than another pachinko, right?