These people won't state anything definitively, but here's an excerpt from the study article entitled "Making Christian Marriage a Success", in the August, 2016 Watchtower. It does make me wonder.
Although the Bible does not provide specific rules about the kinds and limits of love play that might be associated with natural, sexual intimacy, it mentions displays of affection. (Song of Solomon 1:2; 2:6) Christian marriage partners should treat each other with tenderness. (Italics mine)
Does this indicate a softening of their antiquated view of oral sex?