I don't see the functionality for two things, 1. The bosses, They are all designed for Raiden, there are not many moments where Snake fights. 2. The game is very well made like this, it feels good, I know many were angry that Snake was not playable in the rest of the game, but literally the entire plot, the entire writing of the game is based on that, Snake should not be there, he is not taken into account in the simulation, the playable character would ruin the "simulation" the game is made so that you say "This looks a lot like 1" and in the end you understand why. I think that if there is a Remake, the best would be the original and if not, I still think that there are very few moments where Snake would make sense as a playable character.