you can screenshot and send fast enough on Whatsapp that it does’t even matter.
Screenshare is more of a video call thing. Kinda like Facetime. Facetime, Skype, etc never took off. If you look at what took off, it’s Whatsapp, Kik and messengers. Group chat trumps all.
Webcamming has been around forever, yet it hasn’t replaced how we communicate via email, texts, and messages. So while BBM has an advantage in screen share I can guarantee you it’s not going to take off that much.