Next Event could be...

[Lambdafish]

at least it's a better idea than Digimon or Pokemon

Agreed, but from the developers standpoint it is equally as unviable. SE needs to build it into their marketing strategy for it to become a thing and that is not up to Yoshi P or the dev team (and honestly SE main HQ won't listen to our requests when it comes to things like this). All previous events except the XIII events have had direct ties to Yoshi P himself, which is why they were able to happen, the XIII one came about because Yoshi P was able to talk to the director of XIII at a convention and the idea came about and XIII-3 was being marketed. There are stories behind all of the crossovers which are far more than "it would be cool to do", most of the less obvious ones are purely by chance.

FFXIII lightning returns - marketing for XIII-3, came about by chance through a discussion at I believe gamescom (could be E3)?
Dragon Quest X - Anniversary of the game, Yoshi P was part of the Dragon Quest X development team (wikipedia has him listed as designer, other sources say other things), and the director of other dragon quest games, which was a big influence.
FFXI shantotto event - I believe 10th anniversary of the game. As the direct predecessor of XIV, many players came from XI, and the dev team know this.
FFXI seekers event - Celebrates the final expansion of XI, the "death" of the game, and almost acts as XIs legacy being passed on to XIV.
Yo-kai watch - Marketing for Yokai Watch 3, came about through an informal discussion over drinks between Yoshi P and his good friend Akihiro Hino