By next year we shall see the result of the Libra development and if its going to be a successful launch, do you think one day we shall see a facebook login button on exchanges like binance? Would you login to it?

I have seen this on websites like medium.com. Worse is taht not only binance but also kraken and bittrex

There's a possibility that it could happen, but we can opt not to do this every website that has Facebook integration can have other ways to sign up and log in, they just want to make it for first time user to sign up and log in, but if this happens I will never use that option.
I wont use this option in the same way. As convenient as it is, but if this function can directly or indirectly affect the loss of my coins, then I do not need this option.