The OS / UI toolkit should be strongly opinionated, making the consistent, happy path easier to develop and making customization possible but with great effort.
But people would claim that it's easier for a company to take a bunch of web frontend devs and have them develop a UI which rides on top the already-existing Electron. Which is why we have such a plague of bloated Electron apps - because companies are lazy and don't care about the end user experience.
I like the idea of trying crazy and new ideas, but this looks like they just thought corners weren't round enough, and that people will pay money for a file manager that has no sharp edges and won't integrate with your OS.
1. Companies will always want to brand their apps with their particular UI styles.
2. In order to prevent the above, the OS would have to deliberately NOT expose the ability for apps to control their own pixels.
Doing 2 means you are making it impossible to support many application types (photo editors, games, etc.).
NOT doing 2 means that app companies will eventually use the same APIs that the photo editor and game applications use.