There have been a lot of rumors and theories surrounding the plot of Avengers 4 over the last few weeks and some of them make a lot of sense, while others are recycled fibs that end up getting debated over and over again. However, there is a new fan theory floating around that makes complete sense and involves the appearance of Kronos of The Eternals in the conclusion to Infinity War. As with all fan theories, we'll take this one with a grain of salt for the time being, but there are some pretty interesting bits of evidence to support this new Avengers 4 idea.
At the end of last month, Jim Starlin participated in a Q&A session at Puerto Rico Comic-Con where he revealed that Avengers 4 would include another one of his characters. Starlin created Thanos, Drax the Destroyer, and Gamora, to name a few, which got fans excited about thinking about who could be next. In addition to the aforementioned characters who have already appeared in the Marvel Cinematic Universe, Starlin also created Lady Death (who the Russo Brothers have already ruled out), A'lars, Eros, aka Starfox, and Kronos as well as many more characters.
The Eternals movie is said to be in development by Marvel Studios and there was a subtle hint at the project in Infinity War when Red Skull mentions Thanos' father A'lars. That hint is one of the many ways that the MCU has been teasing The Eternals film. It was also recently announced that Matthew and Ryan Firpo are writing the script for the project, which means that it's further along than once thought. A'lars may seem like the go to character from Jim Starlin that will make it into Avengers 4, but Kronos makes even more sense.
Kronos helped to build Titan and he is also the cosmic master of time in the Marvel universe. That last bit is the important part. It has been heavily reported that Avengers 4 will include time travel as well as other dimensions that the Quantum Realm will help explain. If Tony Stark and the gang are out altering the fabric of time, it would be pretty logical to see Kronos, who is also Thanos' grandfather, make an appearance in the film, creating some awesome fan service as well as further setting up The Eternals movie.
We're still pretty much a year away from getting any sort of confirmation about Kronos' involvement in Avengers 4, but the evidence does seem to suggest that he could very well be making at least a small cameo like the one that Red Skull made in Infinity War. Ant-Man 2 will further explore the Quantum Realm, which should shed some light on how it will be incorporated into Avengers 4, and that movie opens July 6th in theaters. Additionally, Captain Marvel opens in March, so we will have a better understanding of the final installment of Phase 3 of the MCU at that time. You can read more about the Kronos theory at MCU Cosmic.