Microsoft's Windows Subsystem for Linux is coming to all Windows 10 users (archive):
You won't have to be a tester to try Windows 10's new, built-in Linux kernel in the near future. Microsoft has confirmed that Windows Subsystem for Linux 2 will be widely available when Windows 10 version 2004 arrives. You'll have to install it manually for a "few months" until an update adds automatic installs and updates, but that's a small price to pay if you want Linux and Windows to coexist in peace and harmony. It'll be easier to set up, at least -- the kernel will now be delivered through Windows Update instead of forcing you to install an entire Windows image.
Embrace, Extend... Excite!
Windows blog post.
Previously: Windows 10 Will Soon Ship with a Full, Open Source, GPLed Linux Kernel
I thought FreeBSD already ran in VMs. Is it "just" a matter of integrating with the new "free" setup or something else?
It runs very well in Hyper-V (locally and in Azure), but WSL2 has a bunch of integration hooks. I believe FreeBSD has a 9p-over-VirtIO driver under review, but it's not landed yet. Once this is in, 9p-over-VMBus is a relatively simple change (same messages, different link-layer protocol, but FreeBSD already has VMBus support). That's needed for the transparent file sharing thing (the Windows filesystem is exposed in WSL as /mnt/c, /mnt/d, and so on. In WSL2 these are 9p-over-VMBus filesystems). I think there are a few other glue things that may be needed. I haven't tried it with WSL2, but I believe Linux supports the Hyper-V virtual sound interface, which means that command-line WSL2 applications should be able to open /dev/dsp and make sounds, whereas FreeBSD is missing that driver (I don't care too much about this one, but it would be nice to have).
Last time I spoke to anyone on the Hyper-V team working on this, they were interested in supporting other operating systems, but Linux is the thing customers care about so it's the highest priority.