Two sources:
- If Cryptokitties could take so much computing power in Ethereum network, how can the network support dapps with scale?, and;
- ONO White Paper: Chapter 3 Technical Framework
In the first link, Edmund Edgar kindly listed several scaling options for Ethereum. In the second link, which includes a part of ONO (a messaging app running on EOS) white paper, the author estimates that the blockchain may need to run more than 600 transactions per second for 5 million users of such messaging app.
There are hundreds of millions of Whatsapp users, thus 60000 transactions per second would probably be required for such an app. Would Ethereum network ever be able to support apps with such scale after the scaling updates?