There is something of a standard, just that for some reason, sellers aren't making replacement modules. I suspect that the pill which comes in the Spiderfire P7, is compatible with the Ultrafire C8, and a host of other variants by other manufacturers (Aurora, Smallsun, Yezl, et al). They also appear to use the same tailcap, as you see the identical-looking tailcap being used in lots of places, even on the big WF-500 (not that it's a good tailcap--it's not).
The outer diameter of the threads of my Spiderfire P7 pill, by the way, is 23mm. The flare at the top of the pill is 24mm.
Drop-ins ("52mm") ARE available for the WF-500 and there are a lot of other variants which can take it, and I think is a different animal. The drop-ins for those I see are a lot bigger than the screw-in pill on my Spiderfire. I think the WF-500 may be loosely based on the Mag Industries MagLite, but is not directly/easily compatible from what I know. I personally am not interested in multi-cell lithium cobalt cells (or multiple any cells) unless there's really a compelling reason, so all my f'lights so far are singles.
I think it's a pity the screw-in "C8" type modules aren't being sold, but I think you can buy the empty pills, and the modules themselves seem pretty easy to modify, and I may upgrade my P7 to an XM-L.
The OP is right, the P60 (D26?) module has kind of lived past what it should, meaning it's served us well, but it's long been time for a better standard. The P60 has many flaws for LED's which didn't matter much with incandescents, or even enhanced them, such as bad heat management. The P60 is too long and narrow to provide wide spill (hence they can't very well be used on headlamps, which is why you don't see them--plus the heat issue). And yet it's also too small to provide good throw, LOL. It's good if you're a cop shining a light in a driver's eyes to intimidate them and not let them see your face if they decide to go the distance and sue you and the police department for your harrassment and violation of their rights. Small enough for a cigar hold in one hand while you hold your Glock pistol in your other hand and try to remember not to rest your finger on the trigger like they taught you in training, so you don't accidentally drop someone who hasn't become a threat.
With P60's, most of the heat goes to the (tiny) pill first, THEN to the emitter, and only THEN to the flashlight head, and then ultimately to the body. Lots of times, it doesn't get that far and things overheat. In today's world where there's an emitter which will produce whatever amount of light you want if you have a battery which will drive it, things are pushed to the limit with P60's, and frankly it's kind of amazing that some of these XM-L's are doing as well as they are! Like 12+ watts into a P60... never thought I'd see that as routine!
While I'm at it, manufacturers ought to start looking at "C" width for new flashlights. We need the extra capacity, and the extra current it can provide. 18650's and 16340's are narrower than any self-respecting reflector or head, leading to a complex and asymmetrical flashlight design. Flashlight bodies and heads could be the same width with wider cells. That would reduce cost and increase performance. I personally would like to see SINGLE 26500 lights (C size, AFAIK), as they'd actually be SHORTER than 18650 lights, yet higher capacity and having a smoother shape. Ever try to take 2 or 3 of the same kind of flashlight and rubber-band them together, to see what multiplying output looks like? If the heads are wider than the bodies, it's annoyingly difficult. If they were all smooth cylinders, it'd be easy to "stack" multiples of cells for cheap "lots-o-lumens" (and find a use those extra budget lights you probably didn't need, instead of springing for that next 'big' light).
As to Old4570's post #3, that an 5 x XM-L would have to be driven at 10 watts per emitter--no way. And to Oldie's early assertion that XP-G's would probably be brighter at medium to low currents... now that XM-L's are out, that turns out to be wrong, at least from my direct experience and that of others' I've read with actual experience. I've seen this propogated several times on this board and I wish that belief would snuff out. The XM-L is a fantastic emitter in most arenas, and kicks XP-G's butt at any reasonably usable current. My XM-L at 3 watts is as bright or brighter than my overdriven XP-G at 8 watts! I did side by side comparisons and measurements to make sure that what I was seeing was really true, because it was hard to believe. But it is.
I consider 3 watts nowadays "medium to low" current; even entry level single-die $5 crapola LED lights routinely consume 3 watts (and they're not bright; think of "MXDL 3W" with the "sunny side up egg" LED).
Cree rates XM-L's at "100%" at 0.7 amps, and I think that's at the Vf (which I think is 3.3v!). That'd be 2.31 watts. (Yes they say it's OK up to 3 amps, but they are rated/tested at 0.7 AFAIK.) And they rate them around 280 lumens at 0.7 amps(!!!). That is official Cree data!
So it is a myth that you need to drive an XM-L hard to make it worthwhile over an XP-G. I think we'll see small lights of lower currents cropping up with XM-L's, and they will be more desirable than similar ones loaded with XP-G's.
So let's take 5 x XM-L's, let's say running at 1 amp each, at 4 volts. So, let's just say 4 watts per emitter. I don't have the chart, but let's assume that 4 watts will output on paper around 400 lumens, or at very least close to it, maybe more. Just say 400L.
400 lumens x 5 emitters = 2000 Lumens!
And that's using 20 watts between two 18650's, so 10 watts per cell, or 2.5 amps per cell, which is quite safe for a healthy Li-Ion, being only a draw of 1C. Li-ion I think is generally considered OK up to 2C (not that I'd recommend that)?
So... 2000 lumens, at 2.5 amps per cell, with 2 cells. Does that sound good to you? Show me the flaw in my logic or how five XP-G's (or anything else) would be superior to this at this amount of energy, including price as a factor. Go out and try to find a reasonably-sized 2000 lumen flashlight. You can, kind of. They will be cutting-edge HID flashlights and most of them will cost several hundred US dollars; some will cost $1000 or more. And they will all use two 25500 or 26500 cells (most likely the latter), not that that is a bad thing, but two of those + the guts makes for a really big flashlight.
So, according to my estimates, the world is crying out for a 5 x XM-L 52mm drop-in. And frankly I can't see why it's not made, since XM-L emitters are wonderfully inexpensive (I still see P7's going for more!! What is that!). And yet to upgrade your 5 x R2 52mm drop-in, between the $26 for the WF-500, and the $34 for the drop-in (now up to $60), at say $9 per XM-L star that's an extra $45 cost just to begin the mod--not to mention time and effort! I think they could mass-produce the drop-in for sale at $50-60 easily.
As it is, reports of a well-driven XM-L versus the 5 x R2 DX drop-in, isn't enough to sway me to buy a WF-500 + drop-in. I hear it's brighter and throws better--but by how much? Maybe 200 lumens? From what I'm hearing, I'm holding off until an XM-L or at least XP-G (not XP-E, mfr's!) version is available. If someone wanted to make these by hand, they could have a little cottage industry I think. I don't think even Nailbender on CPF is making them. I estimate the parts would cost about $60, including drivers. Even sold at $120, many would buy them (I wouldn't). But even at that markup, with the cost of the WF-500 included, it'd be far cheaper than any decently sized 2000-lumen flashlight out there.
And Oldie is right about one thing: a 5 x XP-G has been done (saw the CPF page on it yesterday). The one I saw however, I think was built from scratch. The guy keeps tinkering with it and I didn't see beamshots or measurements, but it was impressive. I forget who it was but he put it in a mag-lite and it looked very custom. I think it'd be way easier to modify a 52mm drop-in with driver already onboard... BUT choosing the drop-in would be critical so you get one which drove the emitters properly (I saw a 5 x Q3 drop-in at Tmart rated at only 5 watts[?!]; maybe they meant 5 amps?).
<Sigh> Maybe I can inspire someone on the 5 * XM-L : ) .
And maybe I can inspire a mfr to start making single-cell 26500 flashlight hosts with interchangeable emitter modules.