Allot of things seems to add up that the "event" is probably Klingon related.
Hints:
- Nicholas Meyer's involvement and the quotes about how the new show would have broad parallels to Star Trek VI.
- Reports that one of the characters in the new show will be a Klingon Captain which implies a strong Klingon perspective will be explored in the series.
- The show is called "Discovery" which parallels Star Trek VI's subtitle "The Undiscovered Country".
- The fact that Fuller has eliminated other major powers/organisations such as the Romulans and Section 31, or the battle of Axanar.
If I had a guess, the event he is referring to is (in broad terms) the "70 years of unremitting hostility" alluded to In Star Trek VI but maybe more specifically the brush wars that involved The Battle of Donatu V mentioned in arguably the most famous episode of the original series.
From Memory Alpha:
The inconclusive Battle of Donatu V, one of the few brush wars fought between the two powers during theFederation-Klingon Cold War, was fought here in 2245. (TOS: "The Trouble with Tribbles")
The show could be about the aftermath of these brush wars, told from multiple perspectives. A cool tie in could be having the "Klingon Captain" being a younger Chang. Although that is probably unlikely since Fuller suggested we will not see familiar characters until the 2nd season at least.