Part of the revisionist history these days is making IBM out the be hero that was crushed by Microsoft but nothing could be further from the truth. IBM was the lumbering giant that evaluated developers by lines of code produced, had 14 levels of management, and wanted to protect their hardware interests more than anything. Microsoft hated working with them because they sucked. OS/2 was so buggy that the first patch was almost as big as the entire original install.
It has been a while since I read a book on NT kernel - "Showstopper!: The Breakneck Race to Create Windows NT and the Next Generation at Microsoft"
NT kernel was "supposed" to run OS/2 apps and Windows apps. But the NT kernel is of MS making, NOT IBM.
The connection to VAX/VMS is due to MS hiring Dave Cutler, who worked there before.
NT was entirely a Microsoft project. They hired the prism team from DEC and started completely from scratch.
Mach and microkernels were hot at one point despite having many issues with performance.