See my full narrative, explaining why 'quietly' in the original thread: https://news.ycombinator.com/item?id=17728515
The repo has only 9 stars and they haven't even changed the README yet. It's not like it's a big open source Microsoft project they're now sinisterly adding Office code to. And even then, the commit title directly mentions Office.
Check the 0.51-macos branch if you missed it; it's got ~350 changed files specifically to support macOS.
HN title lengths are very restrictive, so perhaps it was unclear, but what I was trying to say was that this repo is likely receiving merges of the very same codebase that Microsoft is using to build their RN Mac apps. This is the first indication of which fork they're using for it (and it's surprisingly not derived from the fork that has 14k+ stars!).
Not Electron involved at all. The point of RN is that it is native; no overhead of running headless Chromium. The fact that Microsoft are putting their weight behind it means great things for RN, desktop, and macOS. They say they've finished rewriting most of their core apps with RN; this is the first indication of the codebase they likely used to target macOS. It's come out of nowhere, too: there's a same-named repo with 14k+ stars, for comparison.
They've revealed that they're using RN for all their main products now, but never explained how they were targeting macOS. This is the repo they must have been using; and surprisingly, it's unrelated to the repo of the same name that has 14k+ GitHub stars.
What's brilliant too is that they are indeed open-sourcing it.
So, an Electron app...