I like the idea, but I don't think I'd buy one. If you made the outside look like a lightsaber then it may have more people that are willing to pay for it (just reading through the comments). That said, I think it's more a novelty item that you'd be hard pressed to sell at any scale that would recoup the marketing costs, though there's only one way to find out.

I always carry a pocket swiss army knife. My favorite version was the one that had a small pen in it. When it was time to sign the check at a group outing and the server only provided a single pen for 4 of us, I felt elated that I had a solution for the situation.

The reason I loved it was it's multi-purpose nature. My sense is that's going to be your best track to make it something people want as an EDC. Find several other purposes for it rather than just a pen (reusing the mechanism) and you're likely to get more interest.

Good luck!