That's certainly what Marvel's mastermind Kevin Feige seems to be saying in this new interview with Wired's Adam Rogers. To be fair, he couches this statement in hypothetical terms — and plans may have to change if the risky Guardians of the Galaxy movie fails.
The whole, candid interview between Rogers and Feige is well worth reading. At one point, Feige says that now that the gamble of teasing Avengers at the end of the first Iron Man has paid off, "I could arguably say what we’re planning for the year 2021... Will that happen? I don’t know. But what we planned for 2015 in 2006 is happening."
In other words, Feige had Avengers 2 in mind for 2015 some seven years ago. (And maybe Ant-Man.) And it sounds like there are plans for whatever big event film could be coming out in 2021, which could be Avengers 4 at this point — or maybe some other sort of mega-event, like some version of Civil War or Secret Wars.
But Feige also says that up to now, Marvel's movie productions have been 75 percent planned, and about 25 percent "bob and weave." And a lot depends on how well Guardians of the Galaxy, a movie based on a comic with a "small, rabid fan base," does. Feige says Marvel's not doing Guardians because the fans demanded it, but because the studio needs to grow beyond its core characters:
Five years ago, looking at our plan, we knew that if Avengers was going to work, the movies had to stand alone... Now we have to prove to the studio that we’re more than just these five characters, these five franchises.
There's also a pretty cogent explanation of why DC has failed to copy Marvel's coherent cinematic universe: They don't have a single person like Kevin Feige calling the shots over there. Definitely check out the whole interview over at Wired.