While everyone is sceptical on whether such a service can reach critical mass to make financial sense, a brand new FB replacement may not be able to do it, However FB itself can certainly give that as an option without hurting their revenues substantially.
I was sceptical on the value prop for Youtube Premium, I am constantly surprised how many people pay for it, if google can afford to loose ad money with YT premium, I am sure FB can build a financial model around a freemium offering if they wanted to.