And I think many fans of both characters would love to see their legacies celebrated in this way. NetherRealm Studios is no stranger to incorporating guest characters from other companies into their games, and have knocked it out of the part with references and fan service each time.
DC and Cartoon Network share a parent company in Warner Bros, who also own and produce the Injustice games, and the series partnered with Nickelodeon before to incorporate their popular Teenage Mutant Ninja Turtles characters into the previous title, Injustice 2.
The idea isn't the most ridiculous thing out there. The popular fighting game series where characters from the DC Universe get together and fight it out. One thing that I think would help draw more attention to both characters and their original media is if they made a guest appearance in a future Injustice title. While Ben 10 has continued to appear in his ongoing Reboot series, his relevance in pop culture has dwindled, and Danny has only made sporadic cameo appearances in Nickelodeon crossover media since his show went off the air. These uniquely powered superhero teens inspired not only me, but many others into a lifelong pursuit of creativity and justice, but they both are sadly ignored in general pop culture. For me, and many other children who grew up in the 2000s, two of those heroes were likely Ben 10 and Danny Phantom. Everyone has their childhood heroes, the ones who teach you valuable lessons and entertain you along the way.