As previously announced, WhatsApp is developing a feature what will allow to use your WhatsApp account on more devices at the same time. Chats will be still end-to-end encrypted because WhatsApp was developing a new method to assign keys to specific devices. This method has been already implemented in the recent few updates for iOS and Android, using a hierarchy of phone identifiers.
This feature will allow you to use WhatsApp from your iPhone and iPad at the same time.
I'm sure the iPad version will be released when this feature is ready.