Interestingly enough, I don't see any metal bands that are out there today becoming a new Metallica or Black Sabbath. I don't know a single song by Linkin Park, Korn or Slipknot, and these are supposed to be the mainstream metal bands. What is the "Nothing Else Matters" or the "Enter Sandman" for these guys - you know, the song that everyone has heard on the radio, even if unfamiliar with the band. Twenty years from now, the new kids out there will not be running to purchase their back-catalog, the way people do that nowadays with Master of Puppets or Led Zeppelin stuff. Also, I don't see a metal band out there that will be able to fill 100,000 seat venues. The one possible exception may be Tool (and that's pushing it), but they play a different kind of metal, and some may categorize them as "alternative". While they are not high in my personal rankings, for a while, I thought that Dream Theater might be able to do it, since some of their music is what people go for, but I don't think so anymore.