I dont know if it would still be metal if it were acoustical or not. If it is played with a symphony is it still? For that you would have to ask Metalica who just put out their new album. Some metal is played real slow too and it is considered some of the hardest music. But all of these are still amplified. I think that it would be real cool if some new band came out and tried it unpluged. The closest thin that i can think of right now is Alice in Chains. I dont know if it is metal or not, probably not, but it is cool none the less.