I guess I am coming up with a bit of a controversial issue.
I’ll post it anyway (here a good place for that, isn’t it?).
I personally believe WhatsApp is the first app to get rid of - personally I have never used it… but: For many smartphone users WhatsApp is one of the crucial apps, maybe THE crucial one to have. Some even need it for professional reasons. For that, is very good that WhatsApp actually is running on an /e/ system. But when installing it, your address book will be uploaded to WhatsApp/FB servers right away.
Therefore my idea:
Why not providing an easily installable (or preinstalled) container that recognizes when s.o. wants to install WhatsApp, which subsequently will be put into that container. The user then should validate each an every contact if it should be made available to WhatsApp (in this case onle the phone number and the name should be share with the WA-address book and nothing else).
The better solution would still be not using it, but like this, users could get a hassle free solution using this application, knowing that they share as little contact data as possible with the company behind and he/she would be enabled to comply much easier with the GDPR (the European General Data Protection Regulation).
And /e/ could set a positive sign to the user: We enable you to use this app, we even protect you as much as possible, but we absolutely needed to put it into a cage - so in time you should better look out for a replacement app…