My fiancee recently brought this to my attention and wanted me to write about it. Based on the technical proficiency of a lot of metal musicians, classical music could easily be transformed into metal. We got onto this topic recently and she mentioned how she would be interested in hearing Beethoven's 5th symphony performed by a metal band. I think it would work quite honestly. Can't you hear a group like Symphony X or Rhapsody of Fire attempting this? It could happen.
So, some other songs I would love to hear attempted by a metal band:
"The Devil Went Down to Georgia"
This could easily be done by a band replacing the fiddle with a guitar. It would lose a little something, but there are bands that could pull it off. We would need a band known for their speed, someone like Children of Bodom, early Blind Guardian, or Sonata Arctica to try this out.
This is an absolute classic song from the 1970's. This is an epic song, both in length and scope. Any power metal band should be able to pull this off. I would look for Kamelot to do it best.
I thought about "Smooth Criminal". The Alien Ant Farm version was interesting, though it would be entertaining to hear a thrash metal band take it. But let's see arguably Michael Jackson's greatest song covered by a group. A death metal version would be truly frightening, and would keep with the zombie theme.
I have heard a couple of bands attempt this. This is my favorite piece of classical music. Nobody has ever really gotten it right though in the metal world. The best was the gothic metal band Aion. Again, a symphonic metal band would do this well.