Thank you Rishio for the well thought comparison! It has served as nice holiday reading and food for thought
Getting by with few harmonicas is something I can relate to, though my approach is quite different. I generally carry two or three different tunings which I play in a handful of keys and modes. I mostly play by myself, and if I run into someone they'll have to adjust. To me, the different tunings are so helpful to give different feeling to the various songs that this makes up for the lack of keys. But as you regularly play with others, being able to play in any key definitely seems like a more reasonable configuration.
There is one thing that puzzles me though: Why don't you set them up to play diatonically in ALL keys? The G-harp and the A-harp overlap, in that both are capable of playing in keys G and D, while none of the three are capable of playing in keys B or Bb. If you would instead use, for instance, ED-tuned harps in G, Eb and B, you would be able to play not only pentatonic scales in all keys, but full major and minor scales, and even some more exotic scales in some keys.
EDIT: Writing the paragraph above I was confused about how EDharmonicas are labelled: I thought of the diagram at the end of your post showed a G-harp! This means the keys you miss are Eb and E. (I write more about this in a later post!)
Another thing that crosses my mind is that most of the points you make in favour for the ED hold for other tunings as well. To keep ALL the advantages you want, without a doubt the ED is a good choice, but as I'm myself not that a skilled bender I can't help but think how I would solve the problem of playing in all keys with at most three harps. The following is thus not to be taken as criticism to your approach, but rather as an account of some personal thoughts that your post gave rise to.
I have recently started to experiment with repeating variations of the following pattern, found for instance in the PowerChromatic:
The above tuning can be played in C, G, D and A (and their respective parallel minor keys) using 1, 0, 1 and 2 bends, respectively. This covers a third of the circle of fifths, so if we accompany the above tuning with harps that use
and
We can now play in any key with at most 2 bends per octave:
Keys A, Db and F require 2 bends.
Keys C, D, E, F#, Ab and Bb require.
Keys G, B and Eb get by without any bends at all!
(of course we could choose another partition of the circle of fifths if we are not happy with which keys are the most comfortable.)
Also, none of the keys would have their root note as a bent note, which I with my limited bending skills would be troubled by.
One drawback with doing it this way would be that the range on any one harp would go down from over three octaves to two octaves and a fourth. This could be important for some people, but I'm personally not that bothered by it.
Thanks again for the inspiration, and have a happy new year!