The way I see it, these are the pros and cons of P60:
Pros:
1. Interchangeability. This, of course, is the big one. You aren’t stuck with a specific emitter and/or reflector in a light. Sick of that violet-blue cold XM-L2? Throw in something with a warmer tint. Want more throw than that XM-L2 with an orange peel reflector? Get an XP-G2 with a smooth reflector.
2. ‘Future Proofing’. This follows from the first advantage. Think of how many lights you no longer use because they are obsolete. You can bring an old, favorite light back to life with a new drop-in.
3. Availability of exotic emitters and emitter configurations. Want to run a high CRI XM-L2? Except for a few Armyteks, I know of no light that uses this emitter. Also, if you want to run multiple Nichia 219s, few lights run this configuration. And those that do certainly don’t come cheap. On the other hand, P60 drop-ins using these (and other) less popular emitters are relatively cheap and available.
4. Ease of use. Anyone can swap a P60. And even if you want to build something custom, it’s generally easier to build your own P60 than it is to mod a light.
Cons:
1. Poor thermal management. This is the BIG one. The P60 was originally designed around incandescent bulbs. So to say that heatsinking wasn’t a concern is certainly an understatement. Sure, you can improve things with aluminum foil, copper tape, and strips of aluminum from beer cans. But it will NEVER be as good as a conventional light.
2. Host/drop-in incompatibility. Although P60 is often considered a ‘standard’, the fact remains that it is far from universal. Some hosts simply won’t accept some drop-ins.
3. Increased size. The size of the drop-in basically dictates the minimum size of the light. It would be impossible to make a light of the size of, say, the SC62w that uses a P60 drop-in.
4. Limited host availability. For all the P60 drop-ins available, good hosts are a good deal harder to find. Furthermore, many battery configurations simply aren’t available (or, at the very least, are hard to find). Looking for a P60 host that uses 4xAA? I don’t know of any. Even 26650 hosts are quite rare.
That’s all that I can think of for now. So are P60 lights obsolete? Depends on what you want. If you want maximum lumens, then you should look elsewhere. But if you want a versatile light that can easily run many different emitters and emitter combinations, the P60 lights are unbeatable. Yes, output is limited. But you can probably still run something in the neighborhood of 2A to an XM-L2. And this is good for 600-700 lumens, which ample for the vast majority of situations in which people use a flashlight.