You lack imagination. This is not some crown jewel only achievable by Apple. In the open source world we have tools to convert ext file systems to btrfs and (1)

You lack imagination. This is not some crown jewel only achievable by Apple. In the open source world we have tools to convert ext file systems to btrfs and (1) you could revert back; (2) you could mount the original ext file system while using the btrfs file system.