Problem with ribbon tweeters is that the mid range unit needs to be very fast to keep up with them. I have yet to hear a two way that sounds coherent, because the mid/bass driver is always too slow.
So the ideal setup would be a 3 way that uses a very fast 3" or 4" small midrange unit, then the bass driver can be a good 6" or 8' or even 10" unit.
Cheers George