Cross Over Idea: Devil May Cry
So I got this idea while talking to my friends and we thought it would be extremely dope to have a Final Fantasy XIV X Devil May Cry 5 event with rewards being weapons from the Devil May Cry series.
GNB gets Nero's Red Queen
DRK gets Dante's Rebellion
WAR gets the Demon sword Sparda
SAM gets Vergil's Yamato
MNK gets Beowolf
BLM/WHM gets V's staff
SUM/SCH gets V's book
MCH can be called Pandora (from dmc4) and be one of its 666 forms
DRG can have a variation of Shadow (dmc1 & 5) since shadow would poke/impale His enemies
RDM can have a variation called Griffin (DMC1 & 5)
PLD can have Alastor
Hair styles based off of Dante, Nero, Virgil, Lady and Trish
Clothing would consist of the DMC5 versions of Dante, Vergil and Nero's jackets, pants, boots and gloves along with an option of Nero's Devil Breaker gauntlet.
Those were just some reward ideas from of the top of my head. Essentially it's up to SE how they implement it.
Actual event wise the warrior of light can assist Dante & Nero in slaying a variety of Sin Eaters through the first with the the final battle being a solo instance with the warrior of light assisting both of them facing a sin eater version on Urizen (DMC5)