So originally I was going to do a list of characters I feel need to appear in the Arrowverse, but with the exceptions of Doctor Fate and Zatara they were all Young Justice members. So instead I have decided to put forward my case for why I feel the Young Justice team either needs to make an appearance or have its own series as part of the collective universe.
1) The Arrowverse Already Has Established Members.
The Arrowverse has already established Roy Harper aka Arsenal and Wally West prior to being Kid Flash. Now as fans of Young Justice will know; Roy Harper is a very arc-centric character given that for most of the series the Roy Harper we see is in fact a clone created by Cadmus. While I'm not saying they should make it so Colton Haynes has been portraying a Roy Harper clone for 3 years it is feasible that maybe The Calculator had him cloned and that is the one who returned this season. I think also the identity crisis would be a great acting challenge for Colton Haynes and a way to get him back in the Arrowverse.
Now with Wally, I think it would be a great way of going from a secondary character on The Flash to a main character potentially in his own series. However, as I mentioned to someone when he was cast, I do think Keiynan Lonsdale would have made a great Aqualad but I guess if they're going with the West Family being black in this universe then it makes sense.
Also with what happened in this week's episode of The Flash it is possible that we will see him become Kid Flash soon, so why not give him his speed, let Cisco designate his name and costume, and let him join the team?
2) Other Team Members Can Easily Be Introduced
Martian Manhunter has already been introduced in Supergirl; while it was established as on another world, we have seen that crossing worlds is quite easy when you have the technology. So it is possible for Miss Martian to be introduced, Homo Magi have already been mentioned in Arrow by Damien Darhk so it stands to reason that inserting Zatanna Zatara wouldn't be an issue. Also with both The Flash and Legends of Tomorrow tackling time travel, it makes sense to at some point introduce Bart Allen aka Impulse who is the grandson of Barry Allen aka The Flash.
3) The Arrowverse Could Grow Exponentially
Just as Miss Martian could easily come from Earth-3, Aquaman has already been mentioned as existing on Earth-2. If they were to introduce Atlantis then that could create its own series anyway but introducing Aqualad, Aquagirl, Tempest, Lagoon Boy, the Atlanteans in general would be a great leap forward. Also if they were to introduce Wonder Girl then you have the Greek Gods.
4) A Chance to Change the Roster
What the Arrowverse has done is introduce new young vigilantes; for the moment we have Jesse Quick and Evelyn Sharp aka the new Black Canary. Now while neither of them are members of the Young Justice team, there are certain members we may not actually get on the small screen such as Batgirl so why not replace them, even bring in Raven as she was already slated to appear in the cancelled TNT live-action Titans series along with teammate and Young Justice member Beast Boy.
5) The Effects Would Be Spectacular
A live-action Young Justice series would be an array of characters with stellar visuals. Aqualad, Beast Boy, Kid Flash, Miss Martian, Raven, even Zatanna. All of them would have brilliant special effects; Beast Boy & Miss Martian would look visually unique also allowing for their shapeshifting abilities, while Aqualad, Kid Flash, Raven & Zatanna have visual stunning attacks. This could be the only negative as to why the series may not happen because of the CW's budget and the expense of the visuals.
6) It's Giving the Fans What They Want
I think since the Teen Titans animated series came about, fans have wanted to see a live-action version of them. Now while I'm pitching for Young Justice rather than the Titans, I think if we got a live-action Young Justice series then that would hopefully satisfy the fans who have been pleading to see them in live-action, myself included, especially if it means seeing some fan-favourites in all their glory.