Thinking a new social network platform is destined to fail because it's a copy of something, but without the impetus that produced the original.It's the "make something people want," but more "make something they use for X." You need the original purpose. It has to be to make something that isn't itself. Myspace was mainly novelty and music, Facebook was for status minting from ivy colleges, other ones are for an exo…
I feel like you are right about the need for an original purpose. And would add that at such a momentous time when everyone can see the consequences of private, centralized media selling attention so efficiently, is it really impossible that the situation rises to that level of original purpose? The seed of a new community might just need a great spark.