Personally, I think it's interesting that the blog is no longer on a Mozilla webserver but on medium.com. That aside the article is worth reading:
For example, the prototype we’re feeling good about right now is built with Electron and React, not Gecko and XUL (our go-to technologies for building browsers). For a small team starting out pursuing a new product concept it’s a great choice — Electron is a wonderful tool for us to do prototyping with…
This sounds very much like the approach adopted by the Vivaldi team and has some merit: XUL is probably at the end of its life as a GUI framework. With the release of Positron this presumably means that they can go back to running Gecko as the renderer if they want.
I guess what everyone is worried about is why the need for a rapid-prototyping environment for the browser's chrome? Well, apart from the "who moved my cheese argument" for some of the "improvements" to the desktop browser, the big argument will be the continuing rise of mobile use and wanting to have the same codebase for the various versions and using the principles of responsive design to manage part of this. Seems reasonable to me.
But Mozilla does have to worry about focus and feature creep. It has, in my opinion, done the right thing and dropped side projects such as Thunderbird – nobody at Mozilla wanted to work on it – it should now work hard at avoiding picking up new side projects.