So, if it is liquid, what year is the game set on?
Asuming it's the "old ambulance" theory, when is the Phantom Pain taking place? Does Liquid age as fast as Snake? Is it before Shadow Moses and just a dream sequence (which explains why it's the wrong arm)?
The only dream sequence I remember from any Metal Gear was the dream sequence in Snake Eater, which to be honest, didn't have much to do with anything. It was more of a fan service Kojima did to some of his favourite games of old. Just like he added the Poyaan missions in Peace Walker...
To be honest, I have quite a hard time buying the "it's Liquid theory".
I think it's big boss, the phantom pain is not only for his missing arm (I do not recall Big Boss losing an arm in the metal gear canon), but also from the people he killed. Volgin, The Boss, etc...
Also, I would love the sorrow to return as well.
And by the way, does anyone know what happens to the son that The Boss gave birth to in the battlefield? Who is he? Does Jack (aka Big Boss) know?