Some user from neogaf speculating Ground Zeroes is in MGS5 as a prologue, it kinda makes sense:
http://www.neogaf.com/forum/showpost.php?p=45209554&postcount=2268
"Ground Zeroes is the prologue to MGS 5. Just like the tanker was to MGS 2 and Virtuous Mission was to MGS 3. "
Reference to MGS2? similar to the skin of a snake? or just floor? :P
Same soldiers from Ground Zeroes?
People at the VIP section of Konami wearing Phantom Pain T-Shirts, they aren't swedish:
Doctor Kio Marv?
Logo
Same scar?
Volgin?