Corocoro will probably leak tonight.
and it will most likely have the mascot legends.
Every issue of Corocoro that has come out the month after a game announcement, features the mascot legends. So it's likely we will get at least those and probably some minor details.
I agree, we'll likely be expecting the mascot legendaries, and maybe the starters as well since they're usually among the first Pokemon from a new generation to get revealed in CoroCoro after the game announcement.