Almost everybody I know has at least 2 messaging apps installed on their phone. What's to stop people start migrating to Signal/Telegram/Viber/Keybase/etc.. once WhatsApp starts displaying ads?
Telegram - Thought Leaders + productivity Slack - Biz stuff Line - Thai ppl WeChat - Chinese ppl Hangouts - school + free calls Viber - Old way to call WhatsApp - Late adopters Messeger - Sheeple Signal - Privacy people Keybase - Experimental iMessage - Grandmas and Moms Skype - backup plan Kin - Umm