If it's anything like the Linux files inside File Explorer supported they added previously (https://devblogs.microsoft.com/commandline/whats-new-for-wsl...), it'll be using some derivative of Plan 9.

nfs, cifs, virtio-9p? or virtio-fs, whenever that lands.

Windows uses 9P, it uses CIFS.

The Windows disks are mounted at /mnt/c /mnt/d etc

The real issue is being able to read the WSL disk from Windows which you have to access as a network share from localhost

The same way the current implementation does. The news here is not that Windows can run Linux natively, that's been true since 2016.

The current implementation is a shim over the NT kernel. This new one is a true Linux kernel.

Perhaps more interesting then is how the true Linux Kernel works with NTFS without paying the tax that usually comes with the fancy NTFS features

It's obviously not mounting the NTFS filesystem directly, since it's already in use by Windows, so this is irrelevant to how NTFS is normally mounted in linux.