In that case, I doubt if they will ever optimize the write out of data for ext4. They'll just wait and optimize it for butter fs. If it's the popular file system.
btrfs still have a long way to go. It's original timeline was in 2009. Development is quite active, and it's really a revolutionary filesystem. However it's missing the #1 most important thing, a proper fsck tool. If you loose power in the middle of a write, it's quite likely you're partition is toast. Recently in the last 6 months there have been some tools released to help this, but no proper fsck tool.
The issue with ext4 was in a bug fix. I can look up the exacts if someone wants. A few years ago it was discovered that ext4 wasn't properly locking the cache. That was fixed, and that is that fix is what caused fah write times to sky rocket.