The Omnium has been part of the world schedule since about 2009/2010 - probably in preparation for its introduction to the Olympics in 2012.
At Olympic level, the Omnium came in to replace both the individual pursuit and the points race in 2012 and balances the schedule between sprint and endurance events.
The current format of the omnium is a bit samey - the introduction of the tempo race in place of the individual pursuit was a mistake in my opinion - but as with many of the sports we've seen so far this summer, there is a major problem with how the scoring is presented, particularly in the points race.