>>36931280I would have a select range of legendaries appear in Gen 8 in a mini series called "Legendary Quest".
You get to travel (via a poke ride mon like Mega Lati@s) to locations in multiple regions in order to play through a mini quest. You are 'locked' to a small area in order to get the legendary, but can still explore the immediate area.
For example, a Mew quest takes you to Cinnabar Island, where you can explore the Pokemon Mansion to find it. You can also unoffically challenge Blaine in his gym in the volcano. Many Kanto mons are available to catch too.
A Darkrai/Cresselia quest takes you to Canalave City. While there, you can explore the library, challenge Byron's gym, and travel to both islands. You can also take a pit stop at Iron Island to find some Sinnoh pokemon.
After Gen 8's release, Gamefreak then release DLC for more Legendary Quests. Each Quest allows you to explore a small area of a new region, battle a gym leader, and catch some local regional mons.
It would be an excellent way to add more post game content, Pokemon, and battles.