Were this to be true, and they intended immediate death for this whole layer, then a) "Windows Services for UNIX" would never have existed, and b) the famous argument with David Korn over the quality of their port of his shell would never have happened.
In any case, a "userspace personality" such as NT exhibits is not added quickly. The NT design began in the late 80's, and I think that something like a POSIX layer existed from the beginning.
I didn’t say they intended death for the POSIX subsystem, but that it was included to satisfy requirements for government contracts. It had the obvious additional advantage of allowing UNIX software to be recompiled for Windows with minimal changes.
https://en.m.wikipedia.org/wiki/Windows_Services_for_UNIX
https://m.slashdot.org/story/16351
In any case, a "userspace personality" such as NT exhibits is not added quickly. The NT design began in the late 80's, and I think that something like a POSIX layer existed from the beginning.