Well, this change has definitely made its way to my computer. I don't use the "personal digital assistant" part of Cortana and have not done so since day one, and that includes when I was actively participating in the insider program.
I have a "testing account" set up on my computer where I'd set my default browser to Firefox and search engine to DuckDuckGo and up until checking this evening my Cortana searches on that testing account have brought up Firefox and used DuckDuckGo. I had also tested out Google Chrome with the Chrometana extension and that had been working, too. However, since Firefox has stopped being invoked I'm sure Chrome has, too.
I think Microsoft is in for a rude awakening on this one, potentially legal. It seems that they don't learn from history that while setting something like this up as the default is fine, enforcing it is not. I see regulators in a number of venues not being happy, and taking the actions necessary to "persuade" Microsoft to undo this particular piece of work.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story