Personally, I'd really love to hear about the geography of the void, or how its creatures come to be. I view it as basically the same as Runeterra - except having a deep purple color palette and more sinister geography.
I'll give you a guess.
void pls
Ionia. Absolutely. I'm enamored with all things Ionian, especially the characters.
Targon was said to receive updated lores this year,so it is rather likely for them to get an event this year.
Aside from that I think Piltover could really need an event. Its been so long since Piltover got a champion(Vi was the last one,jinx is from zaun) and the place is barely defined.
Targon, then Bandle City. Two places we know little about.
Ionia or Mt. Targon.
I think a Piltover/Zaun conflict has a lot of potential. If we're just focusing on one area, Mt. Targon (Pantheon, Leona, Taric are all from there, and Taric may be retconned to, as well. Depends on his new lore.) could be interesting.
I'd like to see a focus on 
and Noxus. He wasn't in the Harrowing so I think he had other priorities.
I still even think that noxus will need the help of demacia in case of war,that guy can slay & enslave armies...
Another interesting focus would be on the void.
and 
may be nice. It's interesting to know how void beings interact between them
