What changed I guess is that they switched to embrace Linux full on. And now extending it as well. I trust that Linux is safe from extinguishing though - too much of the world runs on it, and free servers are just too compelling.

Not extinguishing perhaps, but appropriating and building upon Linux for their own benefit without giving much back is certainly possible. Google's already done it with Android.

Quite a lot of Google-developed code goes back into the Linux kernel. Look at cgroups - the entire containerization revolution sprung from code Google gave back to Linux.

Did that come out of Android? Google uses Linux itself as a desktop OS too.

Android hasn't led to anything like a mobile Linux. Google took Linux, built Android on top of it, and now owns the mobile space. Apple did something similar using FreeBSD inside OS X.

Microsoft could use Linux in the same way.

What changed is Azure and you can be sure they will do what they can to keep you locked into that ecosystem.

... like all the other cloud providers.

I don't play too much in the MS ecosystem but from what I read they seem to have moved away from the embrace, extend, extinguish methodology. Which is a good thing.

What would Microsoft like you to build? What is a modern Windows app in 2019? They seem to be retreating from even UWP.