Hey everyone, just an update: I saw a problem that was worth creating a general solution for, so I've been working on Keygen over the past ~year since creating this post. It's a simple software licensing JSON API for small- to medium-sized apps that's easy to integrate with whatever payment provider you use.
Check it out if you have time. It's currently in beta, but planning to launch within the next few weeks. I also have plans to launch a sub-product that provides Electron app distribution and auto-updates (with license validation).
If you have an open source project or are interested in a coupon code for a discounted monthly subscription price, shoot me a chat request and I can hook you up.