Deadpool writers Rhett Reese and Paul Wernick confirm the next film in the series will be R-rated, even though it'll be at Marvel. Earlier this year, Disney's acquisition of 20th Century Fox became official, meaning the Mouse House now has the film rights to the various Marvel characters Fox controlled, like the X-Men and Fantastic Four. During July's San Diego Comic-Con, Kevin Feige revealed new movies for both of those properties are in development, though it is unknown when they will actually be released.
As exciting it is to see Wolverine, the Human Torch, and more become part of the MCU after all these years, the Disney/Fox deal raised many questions about the Deadpool film franchise. That series, of course, is noted for its R-rated take on the comic book genre, gleefully incorporating brutal violence, excessive profanity, and other adult-orientated elements that clash with the MCU's four-quadrant, PG-13 approach to filmmaking. Obviously, fans would prefer if Deadpool was not watered down, and even though he now falls under the Mouse House's umbrella, it looks like they're aren't any plans to change things up.

Speaking with EW while promoting Zombieland: Double Tap, Reese and Wernick were asked about what's next for Deadpool. In their response, they stated a third Deadpool movie would in fact be R-rated. Said Wernick:
"We’re always in touch with Ryan [Reynolds]. We’ve got several projects with him in addition to the Deadpool universe. I think the party line and truth is we’re all still figuring it out. Marvel has promised to continue to let us play in the R-rated Deadpool universe, and the hope is that they will also let us veer into the MCU a little bit as well and play in that sandbox. Our feeling and Ryan’s feeling is that it’s got to be the right idea, it’s got to be great… I think once we collectively agree what idea that great idea is we’ll be off to the races. Ryan’s super-busy, we’ve got a lot of projects lined up, but we wake up thinking about Deadpool, and we go to sleep thinking about Deadpool.”

Back in February, no higher authority than Disney CEO Bob Iger went on the record to say
the Deadpool franchise would remain R-rated, although its place in the larger MCU is not a guarantee. There's a good chance the series remains a separate entity, which would arguably be for the best. There's no denying it would be fun to see Deadpool interact with the Avengers, but it could be too great a challenge to successfully blend Deadpool's R-rated sensibilities into the more family-friendly confines of the MCU. Last year's Once Upon a Deadpool was an interesting experiment to show how the Merc With a Mouth could work in a PG-13 setting, but it wasn't an entirely successful one. Going with the hard R fits Deadpool better.

If Reese and Wernick are allowed to "veer into the MCU a little bit," it might be similar to how the first two Deadpool movies veered into the overarching X-Men franchise. The films largely operated independently of the main X-Menmovies, though still contained humorous nods and references (including
cameos from the Dark Phoenix cast). Most assuredly, Deadpool, in all of his fourth-wall breaking glory, would try to comment on the MCU and joke about how the budget wasn't big enough to score any of the Avengers. It'll be interesting to see what ideas Reynolds and company come up with, and sincethe actor is teasing meetings with Marvel Studios, the gears could be in motion for something.