According to a recent blog post on Wabetainfo, WhatsApp has announced that it is working on an audio chats update. The update is in the development and is likely to be rolled out for WhatsApp beta for Android.
Users will be able to initiate audio chats by tapping on a new waveforms icon that will be added to the chat header, according to the screenshot. On how it will work, there is, however, no official communication. A red button for ending ongoing calls can be seen in the screenshot, and there also seems to be some more space. Since that the waveform icon implies that real-time audio visualisation is possible, it is plausible that the area above the chat header may be set aside for the display of audio waveforms.