There aren’t a whole lot of choices for fet driven flashlights. By all means, go for it. I’m just pointing out that the OD’s of the M1 and X5 are very similar so if you think the M1 is chunky then putting an 18650 tube on an X5 will be similarly chunky. The main differences are straight vs curved taper and the flutes of the M1 head.
So, I got curious on what would be the result and worked a little on photoshop. All the images below and photoshop compositions and with all scales and sizes respected, according to the images referenced. Just a quick study of the final outcome, not a technical render - might be not 100% accurate but gives a nice idea.
So, I grabed the X5 head, kept the reflector diameter, increased only the thread diameter for the tube and assembled the exact X6 18650 tube (it could also be the A6 18650 tube. I don't know which of these two would fit better and would give the smaller size). The finished product can be seen below:
Comparison between the newborn "X5.5" or "X5-6", X5 and X6:
(reference image used for both above: http://img.banggood.com/thumb/view/oaupload/banggood/images/57/FB/804e1006-92a9-44e3-909b-ada14f938fff.jpg )
Another comparison (now including premium lights also 
):
(reference used for pic above: http://i.imgur.com/fsvupMk.jpg )
Comparison between X6 and A6:
(reference image used for size comparison: http://i666.photobucket.com/albums/vv21/Henk4U2/BLF%20miscellaneous/2Ti_Clips_zpsflxatmbt.jpg )
Comparison between Convoy M1, M2, X6 and A6:
(images used for size reference: http://i132.photobucket.com/albums/q11/300bhpton/Torches/Reviews/Eagle%20Eye%20X6-SE%20BLF%20Special%20Edition/IMG_7879Large.jpg and http://i26.photobucket.com/albums/c135/BimmerR/IMG_3901_zps7a4fb796.jpg )
With the options that we have available today, the M2 looks the best midterm but being the same size of X6 makes me stick with A6 but sitll wanting a little less flood.
At the end of the day, this X5 reflector + X6 body combo shows the best combination by far: basically an A6 (that is already pretty nice flashlight) with a throwier reflector.
It is still much smaller than Convoys. When you talk about hiking, this difference is pretty important to fit you bag or pocket: it gives you the stellar X5 performance with a high capacity cell in a A6 sized EDC.
Looks pretty nice and made me want it even more 
Guys, this flashlight is already made - we just need to machine a new head! Let's make it happen!
Why are you doning this now
I already want one!
I skipped the X5 because of the low runtime offered by 14500. It was a shame as X6 is one of my favorite light, I use one daily and have another mint in the box :). I’ll buy 3 of these if it will get to production.
I thought about this also. I’d buy one for sure if it existed.
Well. these images are very clear.
Hardware used is clear
Communicating this should be relatively easy!
The only question is, who has ownership of the CADfiles of the X5 and X6?
Is it team Kronos? Or is it Banggood? This could happen fast.
Is it Manker? maybe team kronos that must have good relationship with them judging by posts and reviews can make this nice light come to life relatively fast too!
It looks like a worthy light to pursue!
I think it is Manker .
If they want , they would be able to do this really easy …
Edit : But i don’t think they will work again with us , that’s what they said…
This isn’t a budget light, but the driver, warranty and the care and attention given their assembly is worth a lot, IMO. You can PM pflexpro on this forum with any questions. He might have suggestions for other customizations.
http://www.pflexpro.com/PFlexPRO-Convoy-M1-XM-L2-LED-Flashlight-p/pfp-m1-ap-fc.htm
I don’t think it would be too chunky. The difference would be, I find the X6 too big to carry in my jeans pocket, it’s just too bulky. So it’s a coat pocket only torch for me. Which sadly limits how much I get to use it.
An 18650 tube light like the A6 is perfect for EDC for me in a jeans pocket, but throw is somewhat limited. The X5 Has the throw but not the runtime.
I reckon an 18650 X5 would be slimmer, smoother and more pocket friendly than a Solarforce L2M, but with more throw and output potential. For me it would probably be the ultimate EDC format.
That said I’m quite a fan of the 16650 format, and wouldn’t object to that as an option. Although would mean machining of a new body and alterations to the head. While an 18650 version would only need the head altering as the body tubes already exist, or could be used from another light.
Very cool renderings 
As for the Convoy M2. I have one of these, the head is quite chunky. And somehow bigger than that of the X5, so less pocket friendly for EDC as it feels more bulky. This trend is true with the rest of the body tube and tail cap too. It’s really thick metal and just chunky.
The crenalated bezel also makes it longer and sharper for pocket carry too. And my one at least it an OP reflector. So wont throw like the X5 can.
I also have the Convoy M1, it too is a little bulky and lumpy. It has a bigger OP reflector than the M2 and is IMO the nicer light of the two. As despite the bigger reflector, it actually isn’t really any bigger on the outside than the M2.
I for one would like to see it threaded for the A6 tubes… 18650 for the larger protected batteries, and the more pocketable 18350.
Nice work on the “prototype,” alfas! 
I love my X5 and X6, and your X5.5 looks great! I really like the proportions.
I borrowed your work and added the soon-to-be-released 26650-powered Eagle Eye X7 for comparison.
I used the image here that shows the X6 and X7 together, so the scale should be close.
I think these two look great together! 
It looks great. You know I’d be in.
I don’t have an X6 or X5, but like the idea of an X5 head on an 18650 tube light body.
I might have my history wrong, but didn’t Eagle Eye come out with the X6 design first? From memory they were quite disappointed when they lost out to Manker, and still wanted to work with BLF. Why don’t we ask EE to scale the X6 head down and put it on the X2 tube?
I would buy one, I really like the x5 would love it to have the extra battery life an 18650 would give it.
+1
I don’t see why are we still supporting counterfeit… The only reason we ditched EE was because they couldn’t deliver a driver with enough amps, but still… The quality was better than the X6 made by Manker.
This thread's getting exciting
I won’t buy anything Manker after the A6, so disappointing quality speaking. EE X6, on the other hand, was really well made, so I hope for a X6.5 or X5.6 or whatever it will be called built by EE.
I could never follow along, who owns the rights to the BLF drivers? I was under the impression that it was either the members who designed it or BLF as a whole, but not Manker. Even if the original designers don’t want EE to use either of the BLF drivers there should be enough talent around here to come up with something.
If it was built around the X2 body perhaps X2.6 or X2.5 would be a good name to prevent too much association with the Kronos X5.
Eagle Eye is right up there with Convoy for my favorite manufacturers. Manker seems to do a decent job on stuff they design (with a couple exceptions) but can’t execute well when we stipulate the design. I think future “Kronos” groupbuys may be done directly with Neal/Banggood/Astrolux.
I would suggest contacting the owner of Eagle Eye through his Aliexpress store regarding this matter. I get the feeling he is a small operation like Simon is, but if you can get these images to him maybe he’d be on board.
My dream would be this form factor (X5 head, 18650 tube) plus the charger from the X2R, but that would hurt the aesthetics a bit.
I think it was less “disappointed” and more “furious.” There’s a reason why you can’t buy any EagleEye products on Banggood anymore. I don’t know how much EE blames BLF for that debacle, or if those wounds have healed.