If Marvel wants to adopt any of the modern, Guardians of the Galaxy stories that feature Gladiator-1, Gunn and Kevin Feige will have to make some changes to the source material. It seems that Gladiator is a character Marvel Studios doesn't own, which also probably means that Marvel doesn't own the Shi'ar-2 either. The character first appeared in an X-Men comic so it stands to reason that 20th Century Fox owns his character rights. Admittedly, the Shi'ar and Gladiator have very little impact on what Marvel can do with The Avengers and other Earth-based stories but it does have an impact on what stories can be adapted from Marvel's Cosmic line. If Marvel ever wanted to adapt the Kree-Shiar-3 war or introduce The Annihilators-4, don't expect those stories to include Gladiator or (Silver Surfer).
[image via The MCU Exchange
Here are some other interesting questions from Gunn's Facebook Q&A:
Q: Are there any plans in the works to dive a bit deeper into Rocket's back story, like Halfworld and characters associated with that at all? Or is it too early for me to ask about that?
James Gunn: I have it all worked out, but I'm not sure when it would be the best to go into it. I think it's some great stuff. It's different from the comics.
Q: Would you like to see Nova come to the Marvel Cinematic Universe and tie in with the Guardians? How would you do it?
Gunn: Yes I'd eventually like to see that. How I'd do it would be secret [sic] tho.
-1 Gladiator is a Marvel Comics character created by Chris Claremont and artist Dave Cockrum and is an analog to Superman. His real name, Kallark, is a combination of Superman's Earth and Kryptonian names - Kal-El and Clark Kent. Gladiator first appeared in Uncanny X-Men #107 (Oct. 1977). Gladiator is a member of the Stronian race, being who possess great strength, stamina, flight and durability provided that they maintain unwavering commitment to a single purpose. Should their commitment wain, so to does their superhuman abilities.
-2 The Shi'ar is a fictional alien race within Marvel Comics lore which is constantly battling for supremacy with the two other chief alien empires of Marvel, the Kree Empire and the Skrull Empire. The Shi'ar is both an alien race which seems to have evolved from birdlike creatures and an alien empire who absorbs other alien species and cultures under its rule. For instance, Gladiator's species, the Stronian race is considered Shi'ar after they were conquered. The Shi'ar first appeared in Uncanny X-Men #107 (Oct. 1977).
-3 The Kree-Sh'iar War was chronicled in the 19-part Marvel crossover event titled Operation: Galactic Storm. Published in 1992, this story saw The Avengers become embroiled in an intergalactic war between the Kree and Shiar Empires. The plot follows that the fallout from Kree and Shi'ar skirmishes is causing the Earth's sun to destabilize, prompting Earth's Mightiest Heroes to join the fray. The title of the storyline is an allusion to Operation: Desert Storm.
-4 The Annihilators are a team of cosmic Marvel superheroes consisting of Silver Surfer, Gladiator, Beta Ray Bill, Ronan the Accuser, Quasar Ikon the spaceknight and Cosmo. The team first appeared in The Thanos Imperative: Devastation (Jan 2011) and served to protect the cosmic side of the Marvel Universe after Star-Lord and Nova are seemingly killed in an alternate reality known as the Cancerverse.
Extra Point: Remember back in 2012 when 20th Century Fox was scrambling to hold on to the rights to Daredevil and Marvel Studios made a counter offer to extend the rights to Daredevil if Fox returned the rights to Galactus and Silver Surfer? Obviously, Fox didn't agree to that deal and Marvel is now set to launch a Daredevil miniseries on Netflix but it shows that Marvel definitely wants their cosmic characters to come home.