Yes as dimava commented above a PWA would be a great alternative.

> in a way it can be more honest for a developer with any commercial intentions to not open source something while offering paid ways to modify the source code

I appreciate that you made your commercial intentions clear in the comments and I agree that you don't want to walk back your license as it definitely leads to backlash. I think developers (i.e. people on HN) tend to trust open-core models more where there's a clear separation between the core open-source components and a paid offering but I guess you don't have to overindex on those given the general audience of this tool.

I don't know what your ultimate monetization goal is, but in my opinion one realistic path is an one-time only payment of some reasonable amount with the full feature as opposed to subscription (I saw your Stripe link in the source).