event timeline would be a great feature.
for a great inspiration : http://users.suse.com/~coolo/opensuse_13.1/

zabbix event timeline could show event duration as lines and their endpoints as events (and maybe midpoints for unknown flapping ?). clicking on endpoints would provide a popup with major event details and access to other screens (full event details, graphs/data for related items etc).
first popup would also provide acknowledge details & way to acknowledge event from the same screen.

acknowledged events would be visually different from non-acknowledged events (check mark ?).

clicking on the line would provide a popup with a list of all involved events.

it should be possible to select scale for the timeline.
timeline would load event data on demand as user moves it. loading probably would be in blocks anticipating timeline movement. periods for which data is not loaded yet should be clearly indicated.

timeline does not invalidate event list view - it should be possible to use on the same screen timeline and time period slider, as well as see current event list. it should be possible to hide any of these three elements individually.

might also be coupled with graphs, showing graph below the timeline.

goes together with improved event filter ZBXNEXT-410