Easier to get the drop D by using a hipshot than a 7 stringer.

Lots of electric heavy metallers play electric 7 string (bottom string a 5th (do I mean a 3rd, must get another drink?) below the next) and usually they are playing the equivalent of Spanish tuning to a D not to an E, but some to a C. So the bottom string could be B, A, or G.

Not used to play 7 string chords, but "power triads".

Modern acoustics that are similar-ish are becomong more available.