Though it's not due in theaters for nearly two years, Avengers: Infinity War has been the talk of the town lately, what with it getting reconfigured as a standalone movie and perhaps being the place where we're introduced to Captain Marvel. With Captain America: Civil War getting ready to hit home video, the Russo Brothers are starting to make the promotional rounds again, and are using that space to clarify a lot of the things happening with Infinity War and its sequel, which still doesn't have a title—and likely won't until the Infinity War gets released.
First up, in an interview with IGN, Anthony Russo pointed out that Infinity War is being looked at as the grand finale to the first three phases of the MCU. "I can't get into too much detail about who we're introducing, but these two movies are intended to be the culmination of everything that has happened in the MCU since the very first Iron Man movie. In being a culmination, these movies are in some ways going to be an end to certain things, and in some ways, they're going to be the beginning of certain things."
He also discussed character selection for the film, and when asked if they were choosing characters to serve the story or on personal preference he said, "It's a little bit of both, because you always have to make sure that your choices feel organic to the storytelling, and really, you have to sort of structure them in the way that they need to be there. You have to have them, or they shouldn't be in the movie. It's a little bit of a dance between the two, where you have big eyes, and you want everybody included in the movie, but you have to go through the process of... what's the best story that you can tell."
In a separate interview with Cinema Blend, Joe Russo elaborated on the decision to no longer consider the fourth Avengers film Infinity War Part II saying, "We wanted the movie to be very different and distinctive, you know. There's certainly cross-pollination between characters and some story-arcs, but you know, the first movie is very clearly Avengers: Infinity War and, in time, we will reveal what the second film is." When pressed further to reveal what the title for the fourth film would be, Anthony Russo simply stated, "You'll learn that, but not for quite some time."
I must say that it's nice to have a bit of mystery in this era of mapping everything out five years ahead of time. Time will tell, but if I were a betting man, I'd put my money on the title being Avengers: Infinity War Aftermath just because it's dumb.