i wish i had copper coin back here :) Nice Mod btw.
The smallest 18650 xm-l torch, Hmm...
I'm assuming that it's to be driven to full power (@3amps). In that case, the ideal design would entail a copper tube just barely larger than the 18650 cell, with a solid connection between the head, heatsink, and body. The idea here is to use all of the torch to help dissipate heat, so threaded connections would be a hinderance. Like you've planned, using a qtc would definately help to save space, along with a very small reflector or TIR lens to help keep OAL at a minimum. Using the coin, if it's pure copper, seems like a good idea, but I think you may want something thicker with better contact with the body (I'm not sure how snug the fit is now). Interesting mod so far, keep us posted!
looking for a p60 laser module and stumbled upon there copper heatsinks/discs. might be worth looking at.
http://laserpointerforums.com/f64/custom-copper-heatsinks-made-order-42626.html
Why do I get the feeling that you're probably already building one in your head. lol
WWMD? 
I wonder if someone had the idea of making a 1AA powered XM-L flashlight. Since eneloops can be stressed to around 8A draw a good booster circuit could easily deliver around 2A to the led. Don't see a point having a flashlight with runtimes like 5min but heck many things were done just for the fun factor. :)
Before someone try that i'm unaware of any drivers suitable for that operation. I also think it's the cheesiest idea of all. But might be fun. I bet Match does not mind doing one just for the fun factor. Making it QTC enabled might be worthwhile.
"I wonder if someone had the idea of making a 1AA powered XM-L flashlight..."
I did an XM-L AA /14500 powered and it's not a circus's torch , is my current EDC despite the ugly beam due the emitter being undomed...
And just when I thought there is no more light I need to purchase... 
agree , also it led to the next step, the qtc cell...
I see many problems to make a QTC switch reliable in non twistie flashlights. Just switching battery might be a disaster (different battery length). I'm sure somone tought somethng to counter the effect... yes/no/Foy?
I finally got XM-L from lck-led so I finished modding TR-801. Works great, doesnt screew all the way, but that will be fixed in the future (with some switch modifications). I know my soldering skills are not so good, but hey it works and it works great - QTC even with spring in the tail is great for adjusting brightness (stiff spring), I also tried direct drive and it pulls just a little under 3A@4,1V. In the end I used alumunium coin - 20 haliers (old slovakian currency - 0,2 koruna) on which I mounted XM-L.
Pics (yea I really need to get some new reflectors
):
You are right Budgeteer - we need to invent more reliable way to use QTC inside the flashlight... I am using foam rings around QTC, so far so good, but I know that isnt really reliable. Maybe sendwich betwen two plates would be better...
EDIT: I tested it for 15 minutes at about 2/3 brightness and the whole body does get quite hot - around 40-45 degrees C. So heat transfer seems ok.
Looks good, nice job :)
Really a good job. The only problems could be the heat transfer at full power.
Bravo stari!
I knew you'll end up doing it nicely. How's the XM-L tint? I have not tried yet mine. Only the ones form LEDDNA... yellowish to green tint.
Tint is very nice white imho near 6000k - comparison:
first skyray s-a1, second modded tr-801, third c30 (with P4 led):
No color tendency of the corona of any kind?
There's actually a forum devoted to laser pointers?
Foy
???! Yep there is... http://laserpointerforums.com/
There's a lot of action over there. Over 4,000 active viewers? I would have imagined.
mustgetoutmoreFoy
You need a spacer at the led or a o-ring at the lense to do away the donut-hole