The EdgeHTML rendering engine, a fork of Trident, which is a fork of Spyglass Mosaic, which is a fork of Mosaic, will be replaced by the Blink rendering engine, a fork of WebKit, which is a fork of KHTML, which is a fork of Khtmlw. The existence of standards and minority implementations does not prevent the emergence of monoculture. Microsoft knows this effect very well. Contributing to Chromium rather than developing a proprietary component of Windows will allow Microsoft to deliver its proposed standards to the majority of developers instead of a minority.
A web browser consists of two major parts – the UI (Chrome, Firefox, Opera, IE) and the engine (Blink, Gecko, Presto, Trident). One part exists independently of the other. In the case of Edge, the UI is a UWP app and the engine is edgehtml.dll written in C++.
One could say that Microsoft is abandoning its own browser because nobody is using it. This simply does not make sense because the success of the UI can be measured by counting the number of people using it, while the engine’s success can be measured by counting the standards it implements. Now the engine ends and the UI remains because nobody uses the UI – it’s nonsense.
Developers are optimizing their (web) apps for Chrome because they are using its DevTools. IE/Edge F12 Developer Tools have never established themselves as an industry standard. It wasn’t in Microsoft’s interest, which rather invested in Visual Studio HTML & JavaScript debugging tools.
Today’s Microsoft position is different from the position it held 20 years ago.
Microsoft in 1998
Windows 98 was the first Windows version that contained HTML and DVD support out of the box. It allowed running SQL Server 7.0 for reliable business data storage and Office 97 for productive management. Microsoft sold the Windows operating system to PC makers to unlock hardware potential and to businesses as a development platform. When you sell a platform, you are competing with the functions it supports.
Microsoft in 2018
Microsoft is selling its own hardware (Surface and Xbox product lines), renting its own servers and providing services (Azure and Office 365), selling advertisements (Bing Ads), and charging provisions from app distribution (Store app). Windows sales have almost evaporated, and the added value of the in-house rendering engine is gone. When you sell devices, you are competing with user experience.
Adopting Blink will allow Microsoft to focus on web standards (this is where the innovation happens), and a performant Windows implementation will be delivered to the majority of web browser users on Windows.
Most web developers have decided that one open-source reference implementation model is better than many independent implementations arising from one standard. So be it.