Really good question. Standard 7 string tuning is just the most logical extension of standard 6 tuning, I never thought of it as a "metal tuning" as such. Equally logical would be a low A instead of the B making the low strings play like drop D tuning in standard 6 tuning (AEADGBE). But I've often wondered my 7 string players don't go the 6 string bass route and add a high string, instead of a low string, maybe DGCFadg? Would take some thought to get the tensions right (email customer service at Ernie Ball for help tuning string guages).
Also I've just learn of a band called Little Tyree, which is right in your ball park! Very very cool. Their guitar player uses 7 and 8 string guitars in combination with bass thumb techniques and lots of interesting two-handed tehcniques in what I think are just standard tunings.
