I wonder if the move will be that straightforward. A group of like-minded, privacy-aware people might move away from WhatsApp when one user advocates for it, but I am not sure a couple of people leaving a large group of average users would be enough to cause the rest to migrate.
Also, human have limited amount of attention --- if Telegram/Signal cannot make it to the critical mass soon then average users who had been convinced to try the alternatives might eventually revert back to WhatsApp because maintaining multiple chatting channels can be quite annoying at times, especially considering majority of their contacts might still be on WhatsApp and it is just easier to post there.
Also, human have limited amount of attention --- if Telegram/Signal cannot make it to the critical mass soon then average users who had been convinced to try the alternatives might eventually revert back to WhatsApp because maintaining multiple chatting channels can be quite annoying at times, especially considering majority of their contacts might still be on WhatsApp and it is just easier to post there.