Merrick here...

Rob Cohen's so horny for a Medieval action epic called...well...MEDIEVAL...that he's pushing aside Vin Diesel's xXx: THE RETURN OF XANDER CAGE (previously announced, currently in development) to go make it. .

If the xXx 3 gang can wait for Rob to finish MEDIEVAL (instead of finding someone else to direct the film), he might return to direct that project as well.

Cohen has backed out of reteaming with Vin Diesel on "XXX: The Return of Xander Cage" for Sony. Instead, he has signed a deal to helm an event-sized action film that Cohen calls "The Magnificent Seven" in the Middle Ages.
[EDIT]
Regency has kept the script hush-hush, but sources said the action brings together warriors from disparate cultures.

...says THIS ARTICLE in Variety.

A side note: searching for xXx footage on YouTube locates footage unrelated to, and sometimes far more interesting than, anything in the two xXx movies to date.