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 (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall