Liquid Snake. Now that's a name I havent heard in a long time. Unless you count the insane amount of references to him in both MGS2 and MGS4. Not counting the references (or the apparent posession through Ocelot's arm, which was actually just hypnotic suggestion), we havent actually SEEN the character as part of the main cast in any game beyond the one where he died. The newer games, however, are focused exclusively on the tale of Big Boss and how his prequel story leads to the events of the very first game "Metal Gear". Seeing as how we're at a point in time where Big Boss has been taken advantage of and the "Les Enfants terribles" project has already happened, that means that Liquid and Solid aren't just soon-to-be anymore, they're already alive and active. In fact, the lesser-known of the two could just be in the newest game.
In the latest MGS V trailer. We're introduced to a young boy named Eli. At first I didn't care about the character. It wasn't until my brother guessed that it was Liquid that we actually backed up and really got a look at him. First off, look at the subtitle below the character's name:
"A youth who curses his fate" (much like a certain character I know)
Not only that, but look at the character's design. He's not wearing an undershirt, and he has slicked-back blonde hair. I think the fact that he's not wearing an undershirt pretty much screams who he is. Also, the age would be about right seeing as how the year is 1984, and Liquid was born in 1972 (making him about 12 at the time of the game). The final thing to point out is the Liquid vibe I'm getting from this kid: the way he crosses his leg and has that arrogant expression. It tells me he's elegant yet evil (again, much like Liquid). If you haven't already seen the trailer, go check it out for yourself.
If it turns out to be Liquid I will be incredibally happy. Sure, I'd like to see what little Solid would look like at the age of 12, but we'll probably see anyway before the game is over. Between the two brothers, I'm glad Kojima chose the one that we haven't really seen much of.
Although, some people are suggesting that it's Raiden. Which, if you've read his bio and looked at his childhood mugshot, doesnt add up (he was born in the 1980's... which at the very least would make him 4 years old in Phantom Pain). Call me crazy but I think it's safe to assume that it isn't him.