In the eventual realm, I am working with ScanSpeak (Vifa) on a 'new' tweeter in that motor frame. My target diaphragm has the potential of greater specific stiffness than aluminum without the ringing and without the high expense of carbon. Work in progress.
For now, that soft dome (I don't know how soft) was engineered to fit that motor and alleged to be plug-in compatible. Jon, see if Rob can make a frequency sweep for you on both driver types so we can compare and contrast.