3. Making the source available would technically be possible, but I would have to consult with a lawyer for that first on how such a thing would be implemented. But I can definitely see this being a feature for the enterprise plan if the customer is interested in it.
4. XPipe uses JavaFX as the GUI framework. It might not be the most fancy and modern solution out there but gets the job done. It is still maintained, but that concerns mainly bug and security fixes. In terms of new features there isn't that much happening but that's not that bad as the desktop hasn't changed a lot over the last decade. There might be more modern solutions out there like Jetbrains Compose, but the advantage of JavaFX is that it is very stable and mature. There's also a good ecosystem of libraries for it.
5. In terms of license enforcement, it's pretty lenient. You only have to validate the license after at most 7 days, so if you are offline for a period of time it will work fine. If you are working on a fully offline system, there is also the possibility to request an offline license that will not require any internet connectivity. See https://xpipe.io/pricing#faq for that.
6. I try to do my best shipping a stable product. I think most developers would probably want to do that, but in practice it's usually investors or management pushing down from above to get features out quicker. I guess I'm in the fortunate position right now being able to choose my own development pace.