I think WhatsApp is where Twitter was during their Ascend-to-protocol Vs Just-push-Ads phase[1], only that WA is dead-set on not going down the Ad route. IMO their options are whether to become an app platform for businesses(Service delivery, payments, shopping) or to become a user-data source for FB. KIM that they are naturally competing with IG & FB.com in generating revenue for FB Inc and subscription isn't working for them(mostly because of almost zero app-buying & digital payments culture in places where WA is popular).

[1] http://daltoncaldwell.com/what-twitter-could-have-been