As everybody knows the bronze dragons are going to be involved with the timeless isle. Blizzard has stated that they want to revisit old contnet so this is my theory.

For the next exp the bronze dragons are going to be involved but not aa the main protagonist. We are going to.be able to revisit old content as max level thanks to them and even content that is not available anymore (like the opening of the portal or the events of tje war of the sand)

This will be the lore explanation to make old content to.fit in the next expansion aside from the main story