The rest of the screenshot looks to be an expansion to the feature that allows for the migration between Android and iOS. From the screenshot, it looks like you will not be able to perform the chat transfer at any time. Instead, the process is limited to during the initial setup of WhatsApp. While the screenshot is showing the process of moving from iOS to Android, it’s probably safe to say that going the other way around is no different.
As with many WhatsApp features in development, there’s no word on when this feature will actually be available. No doubt that there are scenarios where this feature will be usefull. But we’re pretty sure the general user will find the chat history transfer between Android and iOS to be the more useful one.