To be pedantic, Windows already supports other filesystems, it's just a feature rarely used for the main disk (network filesystems and FAT memory cards are ubiquitous, of course).
And for those who wants a to live dangerously, there is even a port of ZFS: https://github.com/openzfsonwindows/ZFSin
But yeah, competition could do that so point taken.
Ps. An article made the rounds on HN the other day (can't find it back) that was rather confidently suggesting that it's Defender running in every CloseHandle system call. But it's all an obtuse black box so super hard to actually find out what's going on.