I cannot imagine that students, kids, or half the world where paying 3 usd a month is impossible, will keep using whatsapp when they have to pay a fee. They will look for alternatives immediately. Telegram?
But actually this is a good move. I tried to convince my family and friends to use alternatives, without success. But now I see hope.
Have stopped using FB and IG years ago, was stuck with WhatsApp because of half the world using it.