A lot of what you're suggesting here (prettier, eslint) is on our list, and even in the works - and I hope would reach users soon. Until we improve the experience around the built-in code editor (and perhaps even after), we've found that it's most comfortable for us to work side-by-side with Codux and our IDE of choice.
Codux isn't meant to replace developers, we made it for them (including ourselves). And sure, it gives you a hot-reloading experience, but also much more, like the ability to visually edit your components on stage in the same place you're viewing them.
During the beta phase Codux is free for use, and open source projects will always have free access. In regards to open sourcing the actual project and code, we plan on releasing some of its parts back to the community, other parts will remain closed.