What would be the event after Illya's event?

Nerofest. Babylonia is still a decent ways away

Nerofest, then Haloween Rerun and this years Halloween.

So, in short, Babylonia is still at least a few months away unfortunately

Babylonia is scripted for end of the year because of story reasons.

More importantly, we're getting a rerun of Halloween from last year AND a Halloween event? That's a lot of farming.