Anaconda creates, and depends on, an /etc/fstab with '/' mount point using subvol= mount option. This isn't an immediate big problem, but has consequences whether it's ignored or changed.

Leave it alone and the user can only rescue one subvolume, the one defined in /etc/fstab for the '/' mount point. That's this bug:
RFE: anaconda inst.rescue might need a better design for btrfs

If it's removed, then anaconda inst.rescue crashes. That's this bug:
inst.rescue crashes if /etc/fstab '/' mount point lacks a subvol= mount option (btrfs)