I thought about doing it but not changing LED, but switch the plastic retaining ring for a metal one, then put fins on there connecting to body for heat sinking, consider that's one of the biggest problems magled drop in has.
Download sells such a part for C-Maglites, it replaces the plastic bulb holder with an anodized aluminum. I have used one for an ROP-hi mod (to deal with heat buildup from the bulb) and a Terralux dropin, to allow extended runtime without overheating the of LED (the terralux fortunately has a Seoul emitter, but unfortunately has no temperature sensor like the MagLED, so instead of dimming over time it will start cooking).
IMHO, a really awesome light would be a 3C or 4C MagLED, with the MagCTower, PLUS swapping of the emitter from a Luxeon to a SSC emitter. Doing that would cause the light to be about doubly bright, and the fact that there would be heatsinking would mean that the light would not dim so dramatically throughout the runtime -- as that is a function of temperature. Performance of such a mod woudl be twice as bright as a stock MagLED, and it would STAY bright.
Finally, I would either stipple the reflector, or install a lens with light diffusion to make the light more useful when de-focused (eliminate the donut hole effect). This essentially produces a variable-angle flood light. I actually like the diffusion film as it softens the beam and eliminates a lot of "harsh shadows" when looking at nearby objects.
