When someone eventually sits down to write the history of Xandar, they will no doubt spend a fair bit of time detailing the decimation of the planet by Thanos in his quest for the Power Stone. There must have been an epic struggle, given that the Nova Corps (or what remained of it) was charged with protecting the Stone at all costs and Thanos doesn't take stubbornness well. It would probably have made quite the spectacle.
Sadly, Infinity War was already too packed with action, and as Joe Russo told students at Iowa City High School (via Reddit), so there was no real need to tell that story on-screen:
Because we thought it'd be one too many- there's so many stones he has to collect and you get into a trap and we thought- we knew where it was in Guardians- so it was easy to deal with it off screen.Advertisement
Sadly, that meant we didn't see what happened to Glenn Close's Nova Prime or the rest of the Corps (including John C Riley's Rhomann Dey), who probably deserved better, but leaving it all off-screen does mean something else too. It means we get to speculate about the possibility that that event could be used in future for the origin story of a beloved Marvel character who has been linked to the MCU for a while.
Putting the logistics of showing those scenes out of the way for now, Marvel Studios could actually retrospectively show Thanos' attack on Xandar as the opening sequence for a Nova movie. And that would mean we could see Nova Prime and Rhomann Dey once more on top of finally getting the cosmic character in his own movie.
In the comics (specifically in The Man Called Nova, Rhomann Dey was the only soldier to escape the destruction of his planet by a child of Thanos. He flees to Earth where he finds someone - schoolkid Richard Rider - to take over his role, granting him his powers and allowing him to become the new Nova.
Later, in a new origin in 2005's Annihilation event, Xandar was destroyed again and the Nova Corps were killed off, all except for Richard Rider, who was granted the knowledge of the Nova Force as a means to keep his planet's culture and powers alive. That's most likely where a Nova movie would draw from and this destruction of Xandar off-screen allows for that to happen in Phase 4.
We've seen hints in the past that Nova might be headed to the MCU - and James Gunn has been clear on his enthusiasm to use him, but only at the right time. Perhaps that "right time" qualification was no more than an acknowledgment that he wasn't actually able to use him because of Marvel's existing plans?
Clearly, time will tell. Would you like to see a Nova movie?