Would not work very well beyond 2kHz as your center to center distance between drivers at that frequency (just a guess, I didn't do the math)would create lobing problems and combing artifacts.The full-range and wide-range driver questions come up fairly often, the answer is the same to all of them. C-T-C spacing versus frequency cut off is the same regardless of driver, though you can cheat a little more with spacing between ribbon/planar tweeters as most are much more limited in their vertical axis dispersion as compared to domes...
Greggo