Has anyone else noticed this pattern with all of the box arts for the games? Do you think the pattern will continue for Gen 9?

Gen 1: Air, Water, quadruped Land mon
Gen 2: Birds (Air) and Suicune (both water and a quadruped on land)
Gen 3: Land, Water, Air
Gen 4: Dragons
Gen 5: Dragons
Gen 6: 1 quadruped and 1 flying
Gen 7: 1 quadruped and 1 flying
Gen 8: Two legendaries of the same species
Gen 9: Two legendaries of the same species?????