At some point after that we know we’re getting Guardians of the Galaxy 3 and apparently Spider-Man: Homecoming 3.
Currently, we know that the MCU is planned through 2019 with Avengers 4, and Spider-Man: Homecoming 2.
While Kevin Feige is clear to not discount the possibility of an R-rated Marvel film in his interview with France’s Allocine, his comments that there are no plans means that we certainly won’t see one for more than two years.
We’re going to guess that Marvel has already planned to make more movies than just these, they’re simply not ready to announce them yet, but however many Marvel currently has on their slate, anything that is planned as of now isn’t looking to go R-rated, meaning that it will be years before we ever see an R-rated film from Marvel, if ever.