As we now know, based on a handful of outstanding forum reviews of Surefire's new ML3T combat light, the KX9T head will indeed fit on an M6 body, but will only operate in low mode. Though I suppose it would be a bit unfair to either characterize this as an oversight on Surefire's part, or to attempt to lay any blame at their feet for this apparent degree of incompatibility, it remains, nonetheless, a rather bitter disappointment to M6 owners that this current state of affairs exists. This disappointment is only magnified when you consider just how much better suited the M6 body is to meet the actual power requirements of the KX9T head.
I highly suspect that in two or three years time Surefire will announce the development of an M6LT which will render this issue obsolete. In the meantime, however, two questions come to mind.
1) Will this incompatibility between platforms make it less likely that SF will eventually offer the KX9T head as a stand alone product?
2) Assuming the KX9T head will be made available as an accessory some day, is there a large enough base of M6 owners to justify some industrious CPF modder/aftermarket specialist devising a new M6 tailcap that will allow for the use of high mode?