Extreme programming is no longer relevant. According to the latest annual State of Agile™ survey, less than 1% of the nearly 4,000 respondents stated that they were practicing Extreme Programming, while 94% said they were practicing agile.
Article discusses XP and the importance of keeping its values/principles relevant. Note that Scrum was the leading methodology then (2015), and growing.
Author = Steve Ropa (CollabNet VersionOne)