I'll try to make this short.
DBC, thats a nice little thingy. But you cant compare that to the usual C8 threads.
Pulsar, metal to metal is far better than thermal paste. But I'm sure you know that. It helps of course, but not much.
skyrider, if you get a direct to copper or brass bond of the center heat pad and wrap the dropin tightly, you are good to go. 3A is easy if you always hold the light with your whole hand. Human blood works very well as a heatsink.
matt, you have some good points but some are not so good. First of all: more thermal mass does not mean that the light will cool down slower when powered for the same time with the same power as one with less thermal mass. Thats just wrong. Adding mass does not change the ability of the body to dissipate heat.
Of course you need thermal mass for short bursts of high power. But not mainly because the light will get too hot to hold (you could use gloves) but because you move the point where thermal sag happens. Thats the main reason for copper bonding: more light. Who cares about heat, turbo mode has the name for a reason.
Now for your argument about threads. The pill doesnt rattle when screwed in, thats right. But not because the threads are so tight (you wouldnt be able to screw the pill in by hand so easily if that was true) but because once you fully screwed in the pill and screw it tightly, there is pressure on the threads. A little less than half the area of the threads will be in contact at that point. If you dont believe me, take a threaded rod and two nuts. You can screw them on very easy, now screw them tightly against each other. You wont be able to move them by without tools anymore now.
Ok, that wasnt short. Sue me. ;)
/edit: DBC, to make Sinkpads round, you could solder some thick copper wire to the back. Manufacturers use brass because copper is a PITA to work with, that would boost machining costs. Also, if you reflow, let the emitter cool down slowly. They dont like thermal shocks.
skyrider, its no problem to sand down stars. If the electrical pads come too close to the edge, file them off (I use a dremel for that).