It's possible, but doubtful. The FFXIII and FFXI crossover events (along with the
Dragon Quest crossover event that also took place around the same time) were actually to celebrate milestones or anniversaries in their respective games (the FFXI event was to coincide with the eleventh anniversary of FFXI service, and the FFXIII event was cross marketing connected with the original Japanese and US/European releases of
Lightning Returns - the DQ event was similarly to celebrate
Dragon Quest Online's first anniversary of service. As these milestones have long since passed, it's highly unlikely SE will bring them back again.
But then, I said the same thing about that we'd probably never see a
FFVII Remake in our lifetimes so... stranger things have happened.