Another argument in favor of adding O_NOATIME support to a limited set of utilities (just 'grep' IMO) is that recent 'ext4' file system behavior defaults to a mode where ATIME is updated only once relative to a given MTIME.
For O_NOATIME to be of use, one must care enough about ATIME to add 'strictatime' to the mount options in /etc/fstab. I find this matters to me only in the context of code development where seeing what has been recently viewed or compiled (mainly by me) is of interest. It's ok if ATIME is nuked wholesale on occasion since the usefulness of the value is short.
