The news comes on the heels of Brazil's detention of a Facebook VP, who was held after failing to give up Whatsapp messaging data. Since the app, which is owned by Facebook, encrypts text messages completely between the sender and recipient, it has no records to give to authorities. Brazil also shut down access to Whatsapp back in December, reportedly over similar security concerns. The addition of encrypted voice chat, while a boon for users, could make Whatsapp an even more problematic app in Brazil and other countries where authorities demand access to consumer data.
The Guardian also notes that Google, Facebook and Snapchat have other encryption-related products in the works, but details are light at the moment. Google's VP of security says it's focusing more on encryption -- we might see something similar to the End to End Chrome add-on soon. And while this is just speculation, I also wouldn't be surprised if Facebook takes a few notes from Whatsapp and works towards bundling encryption into chats.