wintermute0
Banned
Well, didn't Snake never meet Big Boss until he was an adult?
And I think Kojima has gone out of his way to make MGSV a lot less fan-servicey than MGS4, and I'm not sure how him meeting young Solid would be anything other than fan service (not that it's impossible to incorporate him into the narrative). But with liquid, it makes sense geographically, and him being a dick to Liquid would probably serve as good character development for both characters.
While I know he said that he's trying to make the games less fanservicey, I doubt this is going to happen to the extent that you think. The Phantom Pain, as it stands now, is... hard to understand for casual MGS fans that have only played the first few games in the series (talking about: MGS 1/2/3/4). A lot of people skipped Peace Walker, and because of that they have no idea what is going on in Ground Zeroes & the Phantom Pain. Adding Solid Snake to the mix will make casual fans of the series hype the game more and therefore add to it's popularity, plus it makes sense... Solid Snake is alive during TPP, and Hideo Kojima has said that he's going to retcon some things in the canon (here).