Has anybody here tried it? Apparently the big difference is that, apart from a wider pitch range, it naturally tends to avoid diatonic playing (major and minor chord intervals) and makes you concentrate mostly on fourths, fifths and octave intervals. And except for the exceptional 1st string tuning, chord shapes can be transposed between all the other strings.

http://en.wikipedia.org/wiki/New_standard_tuning" rel="nofollow - http://en.wikipedia.org/wiki/New_standard_tuning

That's possible in principle but probably it would mean playing with too thick strings. If you just drop tune the strings 2 to 6 by four semitones without changing to heavier gauges the strings would be far too loose. You would need to use heavier strings to retain the tension, so even if you could then recover the desired pitch by using a harmonizer, the feel would be more like you are playing a 6 string bass rather than a guitar. My guess.

Another possibility would be rising the pitch of the 1st string only by the required 4 semitones using a harmonizer, but that could only be done with a midi-like guitar where you could alter the pitch of one string only and not of the other 5 (a guitar with individual pickups for each string). 

I don't see how you could ever use a capo for that. The objective is having the 6 strings tuned as fifths on the same fret (or open of course) so that the chord and scale shapes are regular across the 6 strings.

No, mandolin strings are not any more "trebble" per se than guitar strings, they only sound more trebble because the scale lenght of the instrument is shorter. The typical mandolin 1st string is 0.11 or so, while for guitars we have even 0.09, but a 0.09 on a guitar sounds lower than a 0.11 on a mandolin simply because it's longer.

I guess that if one Mr. Fripp did not find a solution (and possibly more than one string manufacturer would be happy to make custom strings for him if that gave them publicity) it's because there's no solution.

Don't think so. Maybe you are more referring to something like the string locking brackets placed just before the nut in guitars with a tremolo bridge (I have them installed in both my guitars, they help keeping the strings in tune when operating the whammy bar). But they just secure the string from losing tension, that's all, they have no capo effect at all. Any real capo would be on the freatboard, so disturbing the playing of the strings you do not want being capo'd.