What does the Pending Category on the leaderboard mean?

It's for categories that might exist soon but are waiting for multiple valid submissions. Basically a holding place to make sure a run is popular enough to be added as a category before it's added.

Do the regular mods have to ask the super mods before adding categories to the category extensions board?

its a discussion that takes place between the entire verification/moderator team, as well as taking into account community interest.