Wim Dijkgraaf posits an augmented triad tuned chromatic:
DRAW+ Eb G B DRAW D F# Bb BLOW+ Db F A BLOW C E G#
>So: the key of C=E=G# > the key of D=F#=A# > the key of Db=F=A > the key of Eb=G=B
I built one of these out of a Koch 980 in 1971, thinking that to learn this you only need to learn 4 key positions. Later, Richard Hunter published a similar idea (where the harp is tuned to the complete whole-tone scale, not just the augmented triad). He proposed it to Toots Thielemans, and Toots said he didn't think it would necessarily be any better than solo tuning - you'd gain some things, but you'd lose things, too.
The present tuning system - Solo Tuning is the usual name for it - does have one very strong advantage over symmetrical tuning systems like the augmented-triad system or the whole tone system - it offers more type of intervals, with more types of arpeggios and more types of smooth-scale passages when the slide is used.
Why is this important? In jazz, smooth phrasing is highly desirable, and the best way to produce this on the chromatic is to avoid hole-leaps and changes of breath, playing as much as possible notes in adjacent holes, on the same breath (all blow or all draw) and using the slide. Measuring by this criterion, which has more to offer in variety of intervals, the traditional tuning or the augmented-triad tuning?
By using the slide on a series of all-draw or all-blow notes in adjacent holes on a solo-tuned chromatic, I can get -
I count only 24 intervals, limited to only three kinds, and awfully heavy on the major thirds. Not so good.
Of course, we haven't even begun to get into the possibilities using double embouchure (blocking out middle notes and corner switching) for even larger smooth intervals, or the possibilities for stringing together complete arpeggios, substitutions, or even same-breath scales. But my bet is that the standard tuning offers far more possiblities here, too.
I'd rather have an instrument that has more to offer, even if it is harder to master. The twentieth century is about expanding possibilities, not about reducing choices to symmetrical uniformity (unless you like the hammer and sickle, symbol of a 19th-century idea that is finally getting the heave-ho in most parts of the world).