There is still plenty of scope storytelling wise as far as Solid Snake goes. I would like a game that "fills in the blanks" so to speak between MGS1,2 & 4. They could explore the immediate aftermath of the Shadow Moses' incident, what Snake did between MGS 2 & 4 thus showing his ageing disease unfold right before the players eyes. Then there is also the how Raiden became a cyborg ninja & how he rescued Sunny from the Patriots ie the original intended storyline for Metal Gear Rising. Or Kojima could just use a lame excuse like Octocon invented a new gene therapy threatment & reversed Snake's ageing But either way I hope Metal Gear Solid 5 has The Boss as a playable character & certains around her involvement in WW2 as the plot was rumored to be.