Think about it. Les Enfants Terribles took place in 1972. The Phantom Pain takes place in 1984. Snake would be 12 years old at that point. Obviously Hayter won't voice a 12 year old Snake.
Solid, Liquid and Solidus age rapidly! When Snake was 42, he looked like a man of between 65-70 (MGS4). This could mean that Hayter is voicing a 12 year old who looks, thinks, acts, and talks as if he were an 18-21 year old Solid Snake in The Phantom Pain. This could be the game that sets the foundation for Big Boss being targeted by FOXHOUND and the rise of Solid Snake!
So let's say Snake looked like he was 67 in MGS4. That's pretty agreeable, right? Considering he was basically dying of a mix of old age and fatigue by the end of it? If my math is right, Snake's physical and mental age seems to be about ((.595 x Y) + Y), with Y being his actual age. So if he was 12, it'd look as if he'd just turned 19.
Because really, having two characters talk in the same voice from the same voice actors is weird. Hence the hiring of Kiefer Sutherland. (Who BTW I think will do an amazing job)
PLEASE BE TRUE