a new item, supported by agent, is desired - per-process I/O utilization
suggested key - proc.io[<name>,<user>,<cmdline>] (and maybe other params)

text borrowed from ZBXNEXT-494

See:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7c3ab7381e79dfc7db14a67c6f4f3285664e1ec2
http://guichaz.free.fr/iotop/

Of course it would be nice to have this option available for any supported platform.