Marvel might have to have the Merc With The Mouth exist in a separate label on the big screen, like what Marvel Comics did with the Max Comics imprint, but if that means that DP can’t hang out with all of the other characters in the Marvel Cinematic Universe that’s going to be particularly disappointing to fans.
To throw out another folksy saying, Marvel Studios seems to want to have its cake and eat it too by letting Deadpool 3 have the freedom of the R-rating and also exist in a canon that to date has been exclusively PG-13 (and it never became an issue in the X-Men franchise simply because crossovers didn’t become significant prior to the Disney-Fox deal).