Hey Dan and thanks for reaching out!
I’d love to collaborate more with TC39 so that we could make decisions on what to document when and with better reviews. Traditionally, I’ve been focusing on documenting ECMAScript features that are implemented in Firefox as Mozilla is the main sponsor of MDN. It doesn’t necessarily need to be this way, though, and the community is of course always focusing on things they consider important.
If I understand it correctly, new ECMAScript language features start off with their own GitHub repo and are then later merged into the main ES specification. I think it would be interesting to see if such repo maintainers or feature champions would already think about documentation (just like they think about tests) and involve the MDN team early, so that we could outline what kind of docs would be needed on MDN and when we think it is a good time for actually publishing them.
Currently, docs come in quite late in the process (mostly when things ship in Firefox or Chrome). Sometimes we document things earlier, but then specs change or are abandoned (SIMD.js is such a case where we actually added a ton of docs ). But I think there must be some sort of middle ground, and maybe the different feature stages that ES features have can help making decisions there.
As Sheppy and Sphinx mention, there are a variety of ways to get closer to the MDN pages and our community using some of the listed tools and I appreciate y’all coming closer to us!
I can also offer to get involved where spec work happens, so another approach could be to open “MDN docs issues” on specification repos and point me or the MDN team to them, so we can talk about how to proceed specifically for a new language addition and what MDN work would be involved. Let me know what you think about that and if TC39 folks would generally support having docs part of their workflow / spec tasks.