According to WABetaInfo, the newest WhatsApp beta for Android with build number 2.17.105 comes with a pinning feature. According to the source, users will be able to pin chats (not more than 3, at the moment) in next versions. Also, this feature is disabled by default so users have to turn it on in chat settings.
WhatsApp update to bring new 'Pinned chats' feature Tech2 Mobile
WhatsApp update to bring new 'Pinned chats' feature Tech2 Mobile
