We don’t have much details yet, but we have a name for the tournament format!
Big thanks to Cabled for finding this news!
Melee has just updated a new Beta Version 0.3.36.0 where in their change log state that they have introduced the “Core” format for Disney Lorcana tournaments.
Currently there is no further detail regarding this format though considering that only 1 format is listed, it is presumed that this is the format that all tournaments will be played in, which would include all cards that are released in The First Chapter.
More details will be updated once we get more information.