On Monday when I was first aware of this - I was both excited about it, and a bit worried, but probably not for the reasons you would expect.
From what I understand of the blog, the kernel (and subsystem) will unconditionally ship with all versions of Windows - which, to some extent I can understand because that greatly simplifies the process of taking advantage of WSL on your system. All you then need is to install a distro.
However, with every feature comes potential problems, and this is not explored or discussed enough in the wider community, in my opinion. WSL1 was a fairly isolated feature that did very little to interfere with the operation of Windows at large, and I expect WSL2 will be much the same. WSL1 was a system driver that had a kernel-like implementation - I am not sure what WSL2 will be, I expect it will be similar. So the potential issues there are not much of a worry, for me, if it's buggy it's not likely to cause problems if you never use it.
What I worry about, as someone who is training to be a pen tester, is that this increases Windows' attack surface for vulnerabilities. We already have nasty Powershell malware, now we will potentially have the ability to use Linux's own Bash to distribute malware, too. And unfortunately, with WSL, Linux user accounts are not properly secured against base file system access - it's possible to write Linux malware that can encrypt a user's personal files and demand ransom, much like it is possible to do so with pure Windows code, today.
Another issue is that the kernel that will be shipped will also not have been properly vulnerability tested - meaning privilege escalation is another potential huge issue. i.e. if you're browsing the internet, it might be possible to make a Linux system call which is forwarded to Windows which grants administrative access without the end-user's authorization. We don't know if such vulnerabilities exist yet, but it's definitely something to look for in the coming months.
And then there's the Linux kernel, itself. Yes - it is very secure - however, it has never suffered the trial by fire like Windows has. Yes, Android exploits are common, but they're more common for the Android layer, itself, than for its Linux kernel.
Overall - I am actually really excited for this development and I can't wait to try it out - but I think everyone should be cautious when it goes live in (most likely) this year's October update. We'll see what happens.
