The reason this is happening is money and only money.
Wall-street likes the concept of assured recurring revenue. Once Microsoft release its Windows and office subscribers numbers, the MS stock price will go crazy nuts. This has been showcased by other companies such as Adobe, amazon.
I think salesforce success convinced many CEOs to go this way.
Windows going open source.
Its very hard to make open source windows. The reason is there are lots of 3rd party code in Windows OS and Microsoft will have to pay heavily to these 3rd party companies. These 3rd party dont give a sh1t about open source. They want their money.
But its a possibility, if making Windows open source makes more money than currently, then they will do it.
Making it open source is a huge engineering effort...
It will cause too many patent issues, small, big developers and lawyers crying for money and credit.
Linux replacing windows ?
Not going to happen, all those windows apps have been created over 20 years, like photoshop, can't recompile to linux in 1 day. It will take many years.
only money matters, no body is going to fund porting 3ds max, direct x to linux.