TAAS (Twitter as a service). Twitter is bleeding users but they still have name recognition. I could see them setting up a paid service. Big social sites such as Facebook, Instagram, Twitter, etc could get away with a subscription service. Even if a small percentage of those folks were to pay they would make substantially more than they could ever imagine from advertising. Even a free to play model would pay them more than ads. Ads usually is an afterthought when tech companies are trying to figure out how to monetize. Of all the profit models ads usually are the least profitable and can only be profitable if they scale to a high level such as Google, Facebook, etc.