Snorlax should not get a Mega Evolution, because a limited pool of mega evolutions is critical to game balance. Snorlax does not require a mega evolution because of his role as an underused wall. Snorlax is an excellent Pokemon overall and adding a mega evolution would not only be detrimental to the game and the metagame but it would overcrowd the pool of mega evolutions. Pro's idea of Snorlax's ability to wake up on command would make moves such as rest, sleep talk, etc. completely overpowered as it would eliminate the drawbacks of using such moves. Snorlax could restand then you sleep talk in combination with moves such as Giga impact, toxic, or spikes and then be able to wake up and use moves the situation calls for with full PP. Such an idea on a legendary Pokemon could potentially work as the ""ber" tier would receive much more depth from the resultant play and counterplay such a Pokemon would herald. However, an average pokemon such as snorelax should not be given this ability.
The reason I think Snorlax should get a Mega Evolution is because it would bring some cool ideas to the game. For example, you could have to buy the Mega Stone from the owner of the Pok" Flute, only after you wake Snorlax and catch him. Another good reason is it would suprise new players and satisfy long time players. And Snorlax, being the fat, lazy being he is, could have some really good ideas put into his Mega Evolution.
The uniqueness of Snorlax's mega evolution is not in question here. Any pokemon could recieve a mega evolution and bring a myriad of new things to the game. However, each pokemon may not recieve one or else it would make the mega-ebolution pool too large. Snorlax does not require this supplement to his character as much as other pokemon, such as starters, do.