Like much of the unix environment, a type ahead by hitting tab to match the portion of unique command (ie, if two commands overlap, stop at the overlap and let the user hit the next unique key to keep moving forward).
for now, if you goto the 'gluster' interactive shell (press only 'gluster' in shell and enter), this feature (readline) is enabled.
like 'git' does it for its sub commands.
Feature requests make most sense against the 'mainline' release, there is no ETA for an implementation and requests might get forgotten when filed against a particular version.
because of the large number of bugs filed against mainline version\ is ambiguous and about to be removed as a choice. If you believe this is still a bug, please change the status back to NEW and choose the appropriate, applicable version for it.