I picked up a few of these sidemount NeoPixels(SK6812 based) from Adafruit this week. The casing of the LED is 3.9 x 1.9 mm (0.153543 x 0.0748031 inch).
This is something I’ve been wanting for a while now. It’ll be perfect for lighting up a PCB to show the user where to put an NFC card and such. With 1.9mm height, one can use 2mm acrylic to diffuse the light. Looking forward to put this on a PCB!