David Howells of Red Hat has posted a patch today adding statx support to EXT4. Only about three dozen lines of code were needed for adding the statx support. It includes support for statx's "birth time" (file creation time) by reporting the inode creation time. There is also some mapping of some flags to the statx attribute flags.
The patch can be found on the mailing list and hopefully for Linux 4.12 we'll see more file-system support for the extended capabilities of statx.