Okay, random ponderings that I was trying to tell to Monk, but my room's Internet is going to be on the fritz for...probably three more days, because my mandated Internet provider is a piece of crap business that likes to sit on it's hands and take money instead of actually doing their job.
That's out of my system....
This is mostly in the vein of fanfic justification for differing storylines, but it has occurred to me that a case could be made for Ground Zeroes and the Phantom Pain being alternate timelines, if not outright alternate universes. It's a small reason (and it exists for a legitimate, real-world reason), but it amused me to think about.
...It's the weapons.
You see, in all of Big Boss's games (from MGS3 to Peace Walker), he utilizes real world weaponry from Colt, Springfield Armory, Heckler and Koch, Kalashnikov...all of that. The same thing is the case with Solid Snake's games (including the Metal Gear 2D games, which used images of real-world weapons). Then, we have Ground Zeroes and Phantom Pain, which use...
...Arms Material, Geist, Samozaryadnaya Vintovka Tokareva...all of that. And these are weapons in completely different series: no ARs, no AKs, nothing.
Now, the reason this happened in real life is, of course, money: considering the rumors I heard about the financial strain of developing these games, it's doubtful Konami would have shelled out the cash necessary to secure the licenses from each of these companies to use their products in-game (which they have to: artistic usage and renditions of real-world weapons is a very tidy income for these companies, which are already making a killing in firearms and firearms accessories sales). Honestly, I like it: it adds to the feel of the world for me, seeing these original weapons and the companies that produce them.
In game, though, that means one of two things: either every major, multinational arms manufacturer in the world spontaneously changed their names and put out weapons systems that were different from their flagship systems at the same time, only to revert back to the old names and systems again....
...or this is a completely different world from the mainline MGS series. Which could then be used to argue over all the other inconsistencies and bad retcons that this game attempted to make to the other games in the series (not saying the game is bad: next to MGS3, this might be my hands-down favorite MGS game, at least in terms of gameplay. It does attempt to do a lot of canon-welding, however, and doesn't always succeed).
Anyway, that's my headcanon, at least.