This would be an interesting addition to Spectrum and GoJara/Spark. The project weems to be at a very early state and the statement regarding WhatsAPI is not promising. The German text states that WhatsApp has threatend the dev team of WhatsAPI with legal steps. It looks to me like WhatsApp is not eager to allow other implementations of their chat protocol. If the play cat and mouse with the WhatsAPI developers, we can not ensure a working WhatsApp connectivity.
This scenario was basically the reason why Kraken developement was stoped and we moved to Spectrum.im. The later relies on Pidgin libraries where a large community is supporting the chat protocol development. Long story short: If Pidgin or any other big multi protocol client supports WhatsApp, we may work on integrating WhatsApp.
Just for information, here is a report of another Whatsapp open source dev:
So WhatsApp has sent me their lawyers. …They have demanded I stop distributing products which infringe their TOS and IP on openwhatsapp.org, including Wazapp, OpenWhatsapp for BB10 and Yowsup.