I decided to just go for it and try to get this thing prototyped through PCBWay.  I had initially planned to use matte black soldermask and white silkscreen (a la hack for satan), and that's how everything was designed, but when I actually got to seeing prices for the different options, I decided to go with white soldermask and black screenprinting being that it was less expensive then the matte black I originally wanted. I might switch back to matte black if/when I get many of these produced.

It took me 5 edits before PCBWay accepted my design.

The second problem I encountered that caused my design to be rejected multiple times was the need for the soldermask to be inverted. This was apparent to me at first and I had a little trouble understanding what the PCBWay employee was trying to explaining to me, but I eventually figured it out after finding a few instances of others having the same issues. Unfortunately, I had to go all the way back into Inkscape to fix this. 

On the 5th submission my board design was approved and it's being manufactured as I type this. How exciting. 

I probably pulled the trigger to early as I'm already having multiple ideas on how to improve/alter this design. 

I think it would be more fitting (and more meta) to have WS2812b led's on the board itself.

I also think that it would be much more interesting if the add-on took some sort of input from the badge it was being plugged into. After all, the new shitty add on standard gives us two new GPIO pins to potentially stream data from badges to drive pixels on add ons. This seems like a road I should go down. I don't like the idea that there's no way to verify if a badge is sending out pixel data, so in theory this add-on's leds would only light up with specific badges. I'd much rather have a physical switch or some intellegent circuitry to switch between an on-board pixel stream and a badge-driven pixel stream if one exists. 

Something to think about I guess. 

Additionally, I switched to the SAO.69 KiCad footprint, whereas I had been using a generic 2x3 pin header footprint. I don't think this changes much, I just happened to see the KiCad footprint file on the shitty add ons project page and felt I should be using the 'real thing'.

I also think I have too much blank space on the backside of the board. I'm trying to think of something to fill that space.