This is how I always invisoned on what guest characters should appear in Injustice 3 (or a new DC fighting game) by bringing in characters from recent fighting games and bringing them into this new Injustice game
My picks are...
-Spider-Man (Marvel Tokon Fighting Souls)
-Ryu (Street Fighter 6)
-Korra (Avatar: The Legends Of Korra)
-Mark Grayson/Invincible (Invincible/Invincible vs)
The reason why I picked these four is because a couple of reasons one is because Ed Boon said that he wants to see a Street Fighter and Marvel character in the next game
(Possibly meant for Mortal kombat but maybe also Injustice) the other is that with the merger of Paramount we can have an Avatar character in the game and finally we got Omni Man in MK1 so it's likely we'll get Invincible in Injustice
I have come up with how they're stories in Arcade would end:
Spider-Man: (From Marvel/Version of Marvel Tokon)
Arcade ending: In the final moment he was about to face The Champion until a portal opened and sent him from the battle into the world of Injustice after defeating Nekron the Justice League agree to help send him home and hearing The Champion might win he recruits the league to defeat him forming The Spectacular Justice Society
(Still working on the name)
Invincible: (From Invincible vs)
Arcade ending: Fighting against Angstorm Levy he sends Invincible to the Injustice world but acidentlly replaced Mark with Superman and after the defeat of Nekron Batman tries to send Invincible home but sees that his universe is already been conquered by Superman
Ryu: (From Street Fighter 6)
Arcade Ending: One minute he was finishing his spiritual quest the next he ends up in Metropolis seeing his talents and defeating Nekron Ra's Al Ghul tries to recruit him but he refuses and is now on the run from the league of assassins
Korra: (From Avatar: The Legend Of Korra)
Arcade ending: Seeking warriors from other dimensions Nekron resurrected Korra to do his bidding but with her spirit she breaks free and decides to free the world from Superman's regime
Note: Nekron is not confirmed as the main villain so I just decided to use him because it would be cool if they went with Blackest Knight
Now we already know what they're abilities will be Spider-Man web zips Korra's element abilities Ryu's hadoken and Invincible's viltrumite strength and flight
And if your asking about the notes in the 4th and 5th images those are intro dialogues I came up with for them specifically when they face each other Spider-Man vs Ryu and Invincible vs Korra but how would they interact with other characters?
Now I know what everyone is gonna say... It's impossible for them to appear in get it but it is a possibility Marvel and DC had recent crossovers and the Paramount merger could help with a Street Fighter character appearing because of the movie
But that's my opinion what do you guys think?