I agree that the proprietary editor has been a showstopper for what is otherwise a very appealing advance in programming environments; many of us are old enough to have learned the hard way not to base our careers on proprietary infrastructure.

But it's not clear that this new project is a fix for that: there's no license file or licensing notice on https://github.com/asg017/dataflow and no mention of licensing in https://observablehq.com/@asg017/introducing-dataflow. So, unfortunately, under Berne Convention copyright laws (which is most of them nowadays) the software is by default restricted by copyright, and looking at it may put you at legal risk, because access plus substantial similarity is deemed to prove copying.

Now, possibly that isn't their intention; https://github.com/asg017/dataflow/blob/main/package.json does say "license": "ISC", so maybe it's just an oversight. But I'd like to see a much clearer and more unambiguous statement of their intent to irrevocably commit Dataflow to an open source license before touching it.