I dont see the event lasting long without tying rewards to it. Theres no event that has lasting power that doesnt have decent rewards:
previous mentions of Pankration, chocobo raising
MMM is a quick event, but its rewards sucked cock. who really cared about MMM for its drops? weapon owners according to ffxiah: Barkborer 0, Ermine's Tail 100+, Eventreuse 2, Koggelmander 100+ (all blu's since it was an actual good weapon I believe), Onishibari 1, Scheherazade 1, Zaide 33, Zonure 6. Obviously its not the most conclusive evidence of data, but just to compare, both Genesis items, which drop from Kholomodumo, which has pretty mediocre loot (whens the last time you saw a Kholomondro shout, other than Sandy path), 100+ people own atleast 1 of each item.
The mobs ear/ring/torque/head/whatever, some had some utility, but even then, no one really cared enough.
The cests are absolute garbage, I'm not even going to go into details.
When content hit 80, who cared for ZNM"s? A handful of people did, at best, Sanraku became a sad artist, because the loot became obsolete. Theres some care for ZNM's now once again because of the Mythic 99 trial, but even then, Colosseum is pretty much empty.
XI Wiki



