For the investment of selectively ignoring a string and going to the next one, you can
- think of fifths-based scales normally (!!!),
- sound multiple open-string harmonics with the first string either representing the root ("GAD" as Dsus, "AD" as D or Dm), the fifth ("GxD" as G or Gm, or even "GAD" as Gsus2), or even the fourth ("AD" as Asus)...ideas can get crazier from there if you dip into the major-third harmonic too, and
- you get some really nifty options for close chord voicings in the upper register, while maintaining a wider separation in the bass where it does the most good.
Note, too, that in the DGAD sequence you have two pairs of separated fifths available: DxA, and GxD. Why lookee, that's V and I with a G tonic, and I and IV with a D. (Major or minor, again take your pick.)
For fingerstyle (which is really waking me up to some of these ideas), the concept is even more appealing, since notes on these non-adjacent strings can be easily sounded together. And get this: if I take that CGDGAD tuning and add a single Hipshot detuner to the third string, bringing it down to F, the open strings (and thus all those gorgeous open-string harmonics) become CGDFAD...and that gives me two three-string blocks with different Dm voicings (DFA and FAD, all in one octave!), not to mention "FA" as the relative major's root-and-third notes. "FAD" is in fact the exact same intervallic relationship as the standard tuning's top strings, just a whole step lower. As I've been discovering recently, that's a beautiful and useful voicing.
I've been trying to have it all, of course. Melodically, because I first learned relationships in fifths (Guitar Craft's "new standard" tuning and then mandolin), I want to have that available for improvising, and four ascending fifths covers that just about as well as it can be covered.
Next on the importance list is to have useful open-string harmonics for tapping and fingerstyle accents; the standard tuning's "inverted fifth" that puts the root on top is hugely useful in this regard, and having either the m3 or the sus4 below that root, with supporting open strings below that, is great.
Third, Michael Manring has really turned me on to the idea of detuning and retuning during a piece; most people fixate on either the bass and/or treble string for that, but how about turning that idea upside down a bit and having the third string move...between a m3 and a sus4? I think that just might work*.
As yet another item in the mix (as if there weren't enough), I'm fascinated by the partial capo concept, which provides open strings for droning and accents but which does not disturb the string intervals for stopped notes. (So, for example, if for my tuning of CGDGAD I did a partial capo of 220000, I get a true DADGAD on the "open strings", but if I want to improvise, I simply play the notes where they are in CGDGAD. The only "affected" notes are below the capo. That's intriguing, and if there does prove to be a drawback there, it would be that by capoing some strings you do change the available open-string harmonics. Then again, that might prove to be an unexpected tool.)
And finally, there's quite a bit of music for DADGAD out there; just between Davy Graham (who seems to have pioneered it as a solution to playing non-Western music) and Michael Hedges (the Aerial Boundaries tuning is a simple but clever variation, C2-C3-D3-G3-A3-D4, almost a "double DGAD" since there are now three pairs of separated fifths, but at the expense of the CGDA sequence I want), I can certainly say that people I respect consider it a serious part of the vocabulary!
At any rate, I may have to string one of these git-tawr things up and give it a serious test. The idea of a true "standard tuning" that permits logical thinking when improvising, while also permitting flexible changes to open strings and providing useful open-string harmonics, is really attractive, and this idea has more nice features than anything I've seen thus far.
Jeff Cooper had his Scout Rifle; maybe his quest for the pinnacle of generalization just got under my skin beyond the realm of, er, "simple combustion engines". I'd be real happy with that explanation. (I'm not looking for "inventor" status--I'm quite sure that others have been here before--but rather, like Col. Cooper, I'm interested in arranging the best of what others have done, for my own purposes!)
*For those who haven't looked into it: there are considerations of available physical space for the Hipshot Xtender detuners, and it is impractical to simply use detuners on all the pegs of a conventional guitar headstock--they need too much room. Here, I'm looking at leaving roots alone, and featuring two mid-scale notes instead...although I may also consider a 6th string Xtender, to allow the really nice convenience of pulling the C note up to D; for scales that feature a m7, that could even be done during playing to go between the m7 and the root. On a 3-and-3 headstock, one detuner per side should work fine.