I want them to stick to some of the traditions, but not overdo it. When you have 20 legendaries in one game, they arent special, they are just stationary pokémon with above average stats. It use to be going through an eerie location, navigating through a maze before finding the pokémon whose power many fear.
Or thats all just my childhood imagination.
Anywho, I want
2 mascot legendaries
3rd legendary with a connection to the previous mascots, CLEVERLY hidden in some mysterious area like Giratina, who would of guessed his location without a guide or wiki?
3 legendaries forming a trio, but they need to have a sense of "legendary", maybe the legend of them is a secret and you uncover them yourselves in an ancient ruins of some sort.
1 or 2 legendaries for events
I really want them to keep it simple so the title of "legendary" can feel important again. 7 or 8 might even be a little too much, but atleast not as bad as 13.