RE: danglers from S!K, Ellie and Guy mentioned working on something some time ago but I don't know that status of that endeavor. I would certainly LOVE to have them offer my UKE (or a modification thereof) as part of each package

The extension itself and belt-clip would be easy for them to take on.
The sagewood
extensions are quite expensive for the materials/manufacture involved (<$1 leather, <$1 kydex), their profit margin on each is probably huge, but I'm not involved so cannot be sure, and I do not know their margins for labor costs.
The same goes for most firesteel holders that I've seen go for >$10 a piece - those again cost <$1 in materials, basic equipment (oven or heat-gun + rod for the mold + punch for the kydex) and take seconds to produce. The mounting hardware is the most expensive part. $3-4 should be the norm there, but again labor-costs might play a role.
IIRC, the ESEE pouches and MOLLE-back are made in Mexico - Guy would need to find a US manufacturer to keep with his previous principles on that.