Theory: Young Justice Season 4 will introduce the Birds of Prey.

When Black Lightning discovers Aquaman, Batman, Nightwing, Robin, Oracle, Wonder Woman, and Miss Martian are all secretly working together, Barbara points out to Bruce that most of their team is made of former sidekicks who are accustomed to following his orders.

After their talk Barbra seemed dissatisfied with his answer. Also, in the Season 3 finale Wonder Woman steps down as leader of the Justice Leaguers out in space. Whether this means she will be returning to Earth is unknown.

The Birds of Prey could consist of:

Oracle, Wonder Woman, and Black Canary

Oracle, Black Canary, and Tigress

Oracle, Wonder Woman, and Miss Martian

Also, the blond female Legionnaire seen in the Season 3 finale could be Andromeda or Supergirl. Andromeda is a Daxamite, descended from Mon-El’s older brother. Several characters currently seen in other DC TV shows appeared in Season 3 including Vibe and Stargirl.

Superboy joining the Outsiders publicly could result in him losing his secret identity as unlike Superman he doesn’t have glasses to hide behind. People like his former classmate Wendy in Season 2 have noticed that he still wears Superman shirts at 22 years old. The Red Arrow journals from the video game Young Justice Legacy mentions Red Arrow caught a glimpse of Superboy in action, that footage could still be out there.