Jeremy Keith with a fantastic roundup of the prevailing opinions on Microsoft dropping EdgeHTML. This about sums it all up:
Very soon, the vast majority of browsers will have an engine that’s either Blink or its cousin, WebKit. That may seem like good news for developers when it comes to testing, but trust me, it’s a sucky situation of innovation and agreement. Instead of a diverse browser ecosystem, we’re going to end up with incest and inbreeding.