Does this deter him from completing that project? If not, what big features does Redux plan to offer that regular CoffeeScript does not? Using pegjs instead of jison?
We may merge the Redux version in and bless it as the "official" compiler some day, when it matches feature parity, and if the codebase ends up cleaner than the original (both very likely things to happen). Even in the worst case scenario, where no merge happens, we all benefit, both for learning, new features, and shared fixes for bugs, from having two independent compatible implementations of the language.
95% of the language features were supported during my funding period. Since then, it's nearly reached 100% feature parity, and the tooling/interfaces have been much improved. The code is a lot cleaner, a lot smaller, more modular, more extensible, and uses standard IRs.
If you want to try it out, see the online editor here: http://michaelficarra.github.com/CoffeeScriptRedux/ (shameless plug: it was built using my new browser bundler with full minified-JS to CoffeeScipt source map support: https://github.com/michaelficarra/commonjs-everywhere)
For anyone curious about the compiler implementation process, see this recent slide deck from my MLOC.js talk: https://speakerdeck.com/michaelficarra/an-analysis-of-the-re...
I think a huge benefit for Redux will be making the grammar very clean and extensible. I know it's on your roadmap to CS-ify it.
Edit: Oh, and if you're curious, I wanted to play around w/ translating the CS AST to TypeScript AST, but I'd obviously need to add more typing/declaration syntax to the grammar.