Developer read - this is cool. I've used the web editor a handful of times now. Useful when adding some documentation, or searching for particular line of code in a repo. GH’s search is less handy for that.
Since you can't compile stuff, you can't really test all code interactively or write production code, but combined with CI solutions you could maybe develop (somewhat inefficiently) commit-by-commit in a staging environment. Need to check out what these Web Containers are.