There is enough BS in Ionescu's statements to discount most of what he says (at least as quoted).
Yes, WSL is a Linux ABI wrapper for the kernel, but applications still run in userland, just like "real" Linux. The walls between user and kernel still exist. WSL processes can't see Windows processes or vice versa. WSL runs under a window user context and the WSL "root" user can never exceed the win user's rights on the host system. In short, it is at least as well protected as running any native Windows app on Windows or Linux app on Linux, maybe more so.
Most Windows virus tools DO scan ELF files, not sure how real time scanning interacts inside pico processes, but considering it is ultimately the NT Kernel accessing the files, I would expect real time scanning to just work.
Not saying I would run a production asterisk server under it (but I never run Intel server on bare metal - ALWAYS virtual), but for development it would be great. Also could be great for situations where some processes are easier under Linux in a primarily Windows implementation.