It would have to offer something radically not thought of before or an unexpected combination. People go where the people are for the most part and FB is one of those places.
I was hooked on Vine for 3.5 yrs as it was radically different. Simple premise – looping videos, started short video memes. I liked the people there. Not the big shots but the regular people free to do whatever creative thing struck their fancy. But that was the first really new I’d found in a while and I liked it.