Description of problem: btrfs volumes in anaconda cannot be on an lvm partition. It's perfectly reasonable to want to have some volumes be btrfs and some not: This page agrees: https://btrfs.wiki.kernel.org/index.php/FAQ#Btrfs_has_subvolumes.2C_does_this_mean_I_don.27t_need_a_logical_volume_manager_and_I_can_create_a_big_Btrfs_filesystem_on_a_raw_partition.3F In my case, I was planning to setup my / as ext4 and a data partition as btrfs, both within an lvm volume group. Different filesystems have different strengths, but if the btrfs is not on lvm, it's hard to resize partitions between them. I decided the workaround was to use ext4 on the partition which was intended for btrfs, then after installation, umount, then mkfs.btrfs. As the commands are only trivially different for making an ext4 and btrfs filesystem, this limitation seems very silly and artificial.
You can configure this layout manually, either before running anaconda or by switching to tty2 for a console, and anaconda will detect the btrfs volumes and be able to assign them mountpoints. Not every possible filesystem configuration can be created from within anaconda.
I did not know there were these alternate methods. Thanks.