A Mardi Gras mini holiday would involve kissing npcs for one of three necklaces that when combined become a toy that gives you a new dance when worn. Zydeco maybe?
Other activities include a profession daily quest chain to build and decorate the best parade float, gathering flowers or bunting, mixing paint, whatever themes with that profession.
The float with the most completed quests wins.
A side quest line might involve spying on the stone mason guild for the "cheese makers guild" to uncover a Defias plot.
And, an achievement for dancing on a mailbox dressed only in your tabard.