The idea of tuning exclusively to fourths is interesting, but I've been curious to give an all-5ths tuning a try for quite some time now. It'd have a couple advantages over standard powerchords literally ANYWHERE on the neck with one finger, more-or-less parallel 4-note-per-string patterns, and drastically expanded range. Since this is the 7-string forum, i'll post it as a 7-string tuning...
e|-
a|-
d|-
G|-
C|-
F|-
Bb|
The problem here is the range itself; that Bb is an octave and a minor second below standard B. You could boost it all the way up *sarcasm* to a Mesh-approved F by moving the starting note up a 5th to a high B, but that would cal for a REALLY light string, a multi-radius neck, or both.
I doubt I'd be able to get a super-low Bb to intonate correctly on a 25.5" 7-string neck, but some day i might pick up a couple custom guages and try to give this a go. Although, grabbing a 7321xl, drilling out the low-B tuning peg for a bass key, and tweaking the setup accordingly might be more viable... It'd kill for solo performances (Jim soloway, you listening?

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-D