SureFire's M3LT (existing '400 lumen' version) uses the KX9T LED bezel, which is designed for two-stage output operation.
At SHOT Show 2011 SureFire proposed an M6LT, proto-types of which featured the "KX9T-A", which was a single-output 800 lumen LED bezel.
We know that the 400 lumen KX9T bezel operates at 'low output' on models such as the M3, M4 and M6 which lack the M3LT's two-stage TailCap switch.
We know that SureFire intend to release an updated version of the M3LT with significantly higher output (800 lumens).
So I see there are two main routes SureFire can go:
1) new KX9T only operates properly on the M3LT, and new that KX9T-A operates properly on the M3 and M6, and likely the M4.
[people are going to put the KX9T-A on their M4 bodies so at the very least it should be capable of not being killed by four-SF123As]
[this route has two bezels, identical except for the electronics]
or
2) new KX9T operates properly on the M3LT, M3, M4 and M6, producing two-stages on the M3LT and high-output on the M3, M4 & M6.
[this route has a single LED bezel to make things simpler and easier]