Comment 18 for bug 1261175

> Any such d-i component is going to have to warn that the partition on which /boot resides cannot be f2fs, since grub does not support booting from f2fs yet.

Next GRUB 2 release will include F2FS support. The change is so simple it could be easily backported: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1817310

What remains is creating partman-f2fs and moving f2fs-* packages from universe to main.