I'm with Mike, your design is your design if you want to give it away or not is up to you. The DIY kit is a very good idea also BUT how many of us have bought DIY kits from Tandy, then made a copy of the leather and then piecemealed the rest from what we have, I have and I bet almost everyone on here has at one point or another, how many crap holsters get bought at walmart and then torn apart, copied and remade better. Thats how we learn.
If you made the pattern and instructions then you would have an instuction pack and then the same thing would apply, unless you get a copyright which would take you years and lots of money people are going to use it, probably quite a bit.
Then there is the other thing with those of use that can figure it out on our own by looking at your pictures and then it would look Close to yours but wouldn't be close at all because all they have to do is change one thing and then it's not your design anymore.
I don't think I would do anything with it but if they keep bugging you then I would do a pattern pack and sell it on ebay or something, you probably could make a killing.
Just my opinion, I don't make Holsters
YET
Bryan