I recently upgraded my (rooted) Oneplus 3 to Nougat, and Adaway - which modifys the hosts file broke.
I have been unable to get symlinking the hosts file to work because SELinux gets in the way. Unfortunately I appear to be unable to remount /system rw temporarily, presumably due to a large number of processes started from it at boot.
I believe I can hack the ROM to mount /system RW instead of RO, however I'm uncertain whether mounting /system rw or disabling SELinux is less secure. If I disable SELinux, I need to do it permanently - otherwise the hosts file is unavailable.