I think it is very risky, but taking into account that it is Mark Zuckerberg it will be very easy for him to do so, he has the best programmers in the world, he has the money to carry it out, I think he can achieve it, in fact, he has always been a pioneer in terms of social networks.
In addition, everything that represents progress in my case I support, because everything must be routed there, in innovation and be more advanced. Besides, as he is, I imagine that he will supervise each code himself.
So then there would be no privacy with his "end-to-end" encryption, for which the promise was privacy.