The setup and deployment process is definitely the piece of Extensions that killed my enthusiasm. Having a set boilerplate code sample that gets you right into the fire would lower the barrier for entry significantly. I’m not particularly fond of either React or Node but I know they are some of the most popular frameworks for non enterprise level projects, so I guess I’ll have to suck it up.
It seems like you’ve solved the majority of the problems with developing extensions. Given that these extensions are likely going to be personal projects, usability is key as no one wants to code after work on something as difficult as thier day job, or something difficult to pick up for beginners. Supporting a JS framework like React over just straight JS is also critical for much the same reason.
Beyond that I don’t think I can comment any further without getting to use the service.