I've thought this for a while also - the big messaging apps like Whatsapp and Line and Kakao and WeChat are SO BIG and growing so fast already.
More reason to think they might "beat" Facebook is that a) many are already owned by Internet giants, i.e., have tons of resources to drive growth. WeChat is owned by Tencent/QQ and Line by South Korea's Naver. And b) they are Asia-centric where Facebook is weaker. Maybe these "international" players end up beating Facebook on its home turf.
More reason to think they might "beat" Facebook is that a) many are already owned by Internet giants, i.e., have tons of resources to drive growth. WeChat is owned by Tencent/QQ and Line by South Korea's Naver. And b) they are Asia-centric where Facebook is weaker. Maybe these "international" players end up beating Facebook on its home turf.