I understand one of the reasons behind switching Microsoft Edge to a Chromium codebase/Blink rendering engine was to make it easier to update and increase cross-platform portability, as well as increasing its appeal to the end user. However, it is totally inappropriate to allow one company to single-handedly control the backbone of the entire World Wide Web.
Google created the Blink rendering engine in 2013 as a fork of Apple's WebKit in order to facilitate development of its Chromium project. As can be seen in the graphic above, Blink and WebKit based browsers currently dominate nearly 90% of the market share. While it may have helped develop Chromium's unique multi-process architecture, it has also cemented Google's role in determining how web browsers perform their basic functions.
Blink's mission, as written on its homepage, is "To improve the open web through
technical innovation and good citizenship." How is dictating to the software industry just how their browsers should work at the base level "good citizenship"? How does it "improve the open web" and promote "innovation"?
Remember that a browser's rendering engine governs how and where HTML elements appear on-screen, as well as the interpretation of CSS style sheets; any change in that affects the whole user experience. The effect is even more pronounced when almost all browsers share the same engine. A common engine could encourage maintainers of Blink-based browsers to incorporate "non-standard" features that aren't part of the official W3C specifications. This can render websites inaccessible to users of other browsers, such as Firefox.
If Microsoft wants to adopt Chromium's UI, extension framework, etc., go for it. As for the rendering engine, Microsoft should continue to maintain and develop EdgeHTML, and at the very least offer it as an option to users of the new Edge; in no case should Blink be considered "the model" for standards compliance, but rather as one of many different models.
