Dan,
I have given a lot of thought to this. Although the Firesteel on sheath thing is cool - what I find is that in practice if you were to loose your knife (say the sheath broke) you would not only loose your knife but also your Firesteel. I don't make sheaths with firesteel loops anymore. I make danglers with them - because if I loose my sheath - I generally will not loose the dangler.
I have made a lot of sheaths and truly what people want are not necessarily gimmicks but quality. I have simplified my sheath designs and increased my quality and found that people are willing to pay more for my sheaths and comment on them more than before.
Here are the things I would concern myself with:
1) The little things. Edging, stitch evenness, cleanliness of your dye (clean leather before you dye - clean workshop) and so on.
2) Quality leather. The better the leather - the better the end result. I buy my leather from Wickett and Craig. For bushcrafting try 7 ounce or so. They sell sides for 100 dollars routinely that are great quality. You don't need tooling quality - but good quality.
3) A few options for people to choose. I make a belt / dangler option that is the most popular - but another option like a belt / horizontal carry (H) would be good too. However, you have to make the sheath AFTER the knife and thus it takes more time. I would make what is the most popular and charge a premium for sheaths that are out of the norm. It will take more time - and special kit should cost more.
4) Don't think you need a lot of tools. To make good simple sheaths - I use about 5 tools:
a) Good sharp knife
b) #1 or #2 edger
c) Stitch Wheel (5pi)
d) Dremel with sanding drum (or sander)
e) Drill press
f) Burnishing wheel for my drill press
g) Bone Folder
h) Small antler for edging
I) Simple Skiver
J) Strap Cutter
G) English Strap End Cutter
Quality dye (Feibings), quality sealant (Montana Pitch Blend), quality edging (Gum Tragacanth)...
I think you would be better spending your time improving your leather bending than adding gimmicks or items to your sheathing. That is what I have found.
TF