You know that tools like Bootstrap have great features to make good responsive sites. Given this, is it worth it to spend time building a fully browser based social application? or this is a MUST to make mobile app beside it?
Facebook tried it, and decided against it. OTOH they produced React Native, which allows to reuse much of the code while attaining native look and near-native performance.
If I were to design a new product, I'd try to write as little code as possible, and share it between platforms as much as possible. There are few options to do that (and I won't choose Bootstrap for that).