> On a related note: Never ever use the ext4 to btrfs conversion tool! It's horribly broken and causes issues weeks later.
Care to give some details about this and other failures? Part of what makes a FS reputation is not just people telling "it works" but also stories about how the thing crashed and how they recovered from it. IOW, it always works, until it doesn't, and then it still "works" because I can dig myself out of the hole this or that way.
Inspired by the way you can convert a Debian VM to Arch Linux on Digital Ocean, I happen to have been toying with it recently to auto-convert a blank Debian 8.x VM from ext4 to btrfs. Looks like things are fine, but only because the kernel is <4.x and the VM has very little data on it since it's blank.
WARNING: This is a toy. Do not use for production.