WhatsApp will happily ensure that end-to-end encryption works properly. You can likely be sure of that, barring the occasional arm-twisting from a government and/or agency. The value for them is not in the content of your messages, but in to whom you're talking
Imagine the insane mountains of meta-data. Given "sufficient" uptake,this is like being plugged straight into the backbone of the economy, especially the more informal economy. The type of thing which revenue and economic activity agencies.
They're also aggressively onboarding small and large businesses to their hosted platform, i.e. they provide a WhatsApp phone number, chat bots, etc. and the business only pays per message sent/received. Again, that's a treasure trove of meta data.