sounds like a pretty cool idea...

the thing is, jazz is a little more complex musically, with all the minor seven flat 5 chords and junk like that, and metal is complex rthymically, so to combine the two, you get this big load of complex sixteenth note rythyms combined with jazz musical influences. Oh yeah, and say goodbye to the pentatonic scale as well if you wanna do something like this... it just isn't musical enough for jazz...

but dude, you play with this type of thing to see if you want to do it. Like, try taking some jazz piece like Autumn Leaves and adding a metal influence to see if you like the sound. Use a metal drum rythym, a steady bass line that corresponds to the chords of the song. Have a rythym guitar with dist. playing a power chord corresponding to the roots of the chords with a note that is also in the chord, such as in the chord Gmin7 play a g power chord and add the f on the 4th string. Then, just have a lead guitar or singer with the melody. Oh, and speed it up.