If facebook promised to let whatsApp stay as an independent product and not pollute it with ads then why did facebook purchase it in the first place. They are not going to integrate whatsApp as a part of facebook messenger. They might make something else something all together but still a costly price to pay whatsApp to make whatsApp what its already doing. (could be a different reason to take out competition, either way a pretty expensive agreement.)

One thing is sure, any app which connects a billion users, facebook will go after it.