I don't know, how you would get 500+ lumens out of any single LED in existence. They do make LED tower modules for the M3 turbo and M4 that I believe would fit the M6.
It wouldn't be a 'drop-in' if it were any more complex than the existing tower modules; because the reflector and head of the M6 is not meant to be accessible to your average joe.
So even if someone made a 3-LED 'drop-in', you'd have do some heating and opening of the head, removing the reflector and dropping in your 3-LED module.
Not sure what the Osram O-star (6-dies) is rated at, but maybe someone can make a tower module with the o-star emitter and drive it hard enough to make around 500 lumens. The M6's parallel pack will provide a good amount of juice for decent runtime.