Maybe John upon excomunication converts. But that would lead to Runnymede being less likely to be a compromise as it is OTL.French were such deeply Catholic that king who converts to Islam will be deposed and probably killed king. And even more impossible if it happens in 16/17th century.
-Normans of Sicily convert to Islam
-Saadi Morocco, in alliance with England, conquers the Canaries and/or Cuba. The population converts with time but keeps their language.