Now that most have seen Avengers: Endgame, all the speculation has been put to rest. Despite rumors that a "bigger threat" could've come to the MCU or that some older villains might return, the truth turned out to be very different. Endgame was all about the Avengers taking back what they lost to Thanos.
One of the biggest characters in the movie was Tony Stark. There were rumors suggesting that he would put on the Godkiller armor: a suit designed to beat Thanos. He never wore that armor in the film, though, which was a real shame for a number of reasons.
10 CELESTIAL TIES
In the comics, the initial Godkiller armor was a machine built by the Celestials during the Celestial War. It was created specifically to destroy Celestials. The Celestials had some ties in the MCU, including both Guardians of the Galaxy films (with Ego being one himself). However, the Celestials haven't played any major roles in the movies.
By introducing the Godkiller armor, it could've been a way of subtly inserting the Celestials as important to the MCU lore once again, if not teasing what could come in the future. With most of the Celestials gone from the world, though, it might've been hard to integrate them.
9 A JAW-DROPPING MOMENT
There were tons of jaw-dropping moments in Avengers: Endgame, whether it be Thor summoning both Mjolnir and Stormbreaker or Captain America being worthy of the hammer. If the Godkiller armor appeared in the movie, it would've been another jaw-dropping moment that would've left fans stunned long after they saw the film.
While the suit doesn't necessarily have to be massive, there's no denying that it would certainly grab viewers' attention. It's a golden suit that's powered by nuclear energy (at least, the Mark II version that Stark created in the comics is). That would've been another crowd-pleasing, clap-worthy scene in the film.
8 DIFFERENT THAN BLEEDING EDGE
The Bleeding Edge armor was Tony's new suit in Avengers: Infinity War. Created with nano tech, it was the most powerful suit that Stark had ever made, allowing him to take a lot of damage while dealing it out at the same time. Because he gets a new suit in every film appearance, most thought that he'd get a drastic upgrade once more in Avengers: Endgame.
However, the suit in that movie was very similar to the one we saw in Infinity War. Had the Godkiller armor (or a variant of it) been used, that would've served to make Iron Man a bit more visually distinct in the movie.
7 A COMBINATION OF HIS SUITS
Tony Stark built a lot of Iron Man suits, with Iron Man 3 even exploring how that part of his life consumed him. He learned different lessons in battle, which inspired him to make more changes to his armor. The Bleeding Edge built on a lot of that, but Avengers: Endgame seemed to be the time for Stark to have a suit that combined all the tech and variations seen in his previous suits.
In effect, it would put all his knowledge together into one armor in the form of the Godkiller. One could argue that Bleeding Edge already served that purpose, but it wasn't treated like it did.
6 CELESTIAL WAR SETUP
With Avengers: Endgame over and Spider-Man: Far from Home serving as an epilogue to the Infinity Saga, we don't know where the MCU will go from here. While we don't think Avengers: Endgame was the time to gratuitously setup future stories, the Godkiller armor could've served as a neat foreshadowing element.
Perhaps the resurgence of the suit would bring the Celestials back and build toward a second Celestial War. With Phase Four embracing more cosmic elements thanks to movies like The Eternals, it would be a natural progression to see the Celestials become a focal point. Galactus could even get an introduction that way.
5 STARK LEADING THE CHARGE
When all the Avengers return from dust and join the battle against Thanos, it is Captain America leading the charge with his broken shield and Mjolnir in hand. However, with Tony Stark being the MCU's main character in many ways, it might've been more fitting to have him leading the charge. This could be further justified if he had the Godkiller armor.
Have the Godkiller armor activate later in the fight, then the Avengers appear and rally around him. He rockets off the ground with Earth's Mightiest Heroes behind him as he charges toward Thanos. It would've been a great moment, though the one we got was also great.
4 THANOS VS IRON MAN REMATCH
Thanos and Iron Man had an intense battle in Avengers: Infinity War, though we knew that Stark was pretty much doomed from the start. After being defeated and nearly killed by the Mad Titan, we all knew that he was the one who deserved a rematch with Thanos.
He did battle Thanos again in Avengers: Endgame, but he had help the entire time (save for the moment where he snatched the Infinity Stones). Had the Godkiller armor been an element of the movie, Stark could've had a rematch, but the tables would've been turned. Tony could've had the upper hand with Thanos on the defensive.
3 A RACE TO USE THE SUIT
The final battle of Avengers: Endgame had the team searching for Scott Lang's ugly brown van, which contained the Quantum portal that could send them back through time and get the Infinity Stones away from Thanos. This led to the most epic game of hot potato, where the heroes were tossing the Infinity Gauntlet to one another.
Had the Godkiller armor been in the film, it could've served a similar function. Stark was begging the heroes to stall Thanos long enough that he could dig the armor out from under the rubble and get it running so the Avengers could get the upper hand.
2 EXTREMIS TIES
In the comics, Tony Stark created the Godkiller II armor with a modified version of his Extremis armor. Long story short, Extremis was used to save his life and he used it to build a suit that was tied to his body. Extremis was a major component of Iron Man 3, a movie that largely gets overlooked in the MCU's future.
By bringing in the Godkiller armor, it could've been another way that Avengers: Endgame would reference Iron Man 3Â beyond a teenager. It would also feel like the events in that movie served a greater purpose in the grand narrative of the MCU.
1 INCREDIBLE FAN ART
One of the reasons speculation on the Godkiller armor started was because of some fan art that was released for the suit. This fan art was downright stunning, giving the Iron Man suit a golden and cosmic look to it. It's likely that, had the Godkiller armor been used in the movie, it would've been visually different from how it appeared in the comics.
That said, it would've given the animators the opportunity to design the most outlandish version of the Iron Man armor to date. Just by seeing this fan art alone, plenty of people were excited to see if it would make it in the movie.