Ok, so I spent about an hour casually reading the posts, watching the demo videos and glancing at the code. I agree with your premise and I like a lot of the implementation so far. It's great to see more innovation and research in this area alongside Light Table, Eve (which seems to be going in a similar direction with spreadsheets), NoFlo and others.

I'm curious about the goals of the project. If the goal is to replace an existing language and editor pairing then it's going to be an uphill battle (see previously mentioned related projects). If it's to be supplemental with existing development tools then what use cases are you targeting?

Adding this as an optional layer to an existing editor might help work out some of the ergonomics. Performance issues aside, building on top of Atom might be a good choice since it's mostly web based like the current UI in the demos. Similarly, a custom kernel or cell type in ipython might get the ideas into daily use.