The badge count feature is still under development and is expected to be available in a future update. WhatsApp is also working on a number of other new feature, such as the ability to filter chats by custom lists. This feature is already available in the latest beta version of WhatsApp for Android.
WhatsApp Badge Count for Chat Filters. | Image credit — WABetaInfo
In addition to the badge count feature, the latest WhatsApp beta for Android also includes other bug fixes and improvements. If you are interested in trying out the latest beta features, you can sign up for the WhatsApp beta program through the Google Play Store. Although these days it can be very difficult to get a spot as the beta program is almost always full.