I think this a neat idea but personally I probably wouldn't use the service, because I'm one of the people that feels that if someone else does some of the work it's not truly "my" quilt. I machine-sew my bindings...they're not perfect but nobody I give my quilts to would ever notice the difference so I don't worry about it. And the more I do it, the better looking they get. I won a ribbon at the local fair with one of my machine-bound quilts so it can't look that bad.
But I do think there are a lot of people who strongly prefer a hand-bound quilt and either don't have the time or the hand-stamina to do it themselves, so I think it's entirely possible you could turn this into a nice little money-maker. Another potential market might be for old family quilts that need new bindings. Non-quilters would have no clue how to replace a worn binding, so that might be a source of potential customers for you too, if you don't mind dealing with removing or covering up the old binding.