Three more knockoff Neopixels failed in the last few weeks, including one that can’t possibly suffer any thermal stress:
I wrapped the halogen bulb in a shop towel, laid the ersatz heatsink against an anvil (actually, it was a microwave transformer on the Squidwrench operating table), whacked a chisel into the epoxy joint, and met with complete success:
Having epoxied the PCB and braid in place, there was nothing for it but to drill the guts out of the brass cap:
Which produced a pile of debris in addition to the swarf:
The brass cap emerged unscathed, which was just about as good as I could possibly hope for.
The base LED in this 21HB5A also failed:
Soooo I had to unsolder the plate lead and Arduino connections to extract the bottom PCB; fortunately, that was just a press-fit into the base.
I should mount a 3.5 mm stereo jack on the platter and run the plate lead into a nice, albeit cheap, knurled metal plug, so I can dismount both the tube and the plate lead without any hassle. Right now, the tube can come out of the socket, but the plate lead passes through the platter.
For whatever it’s worth, all of the dead WS2812 LEDs pass the Josh Sharpie Test, so these failures don’t (seem to) involve poor encapsulation.
The Smell of Molten Projects in the Morning 
At some point I’d consider making a receptacle for the pixel (I.e. Pin in slot) so they’re easier to replace. Maybe a plug in receptacle in the brass piece and a threaded ring permanently bonded to the bulb that you could then screw the brass piece on to. That’s a lot of work for a gewgaw, though. ;-)
Devoting a whole lot of effort to make a “lasts forever” part replaceable doesn’t (uh, shouldn’t) make much sense. It seems I’m not the only one to get a bad batch, so maybe it’s time to go full-frontal steampunk on those things.