That's unlikely to happen as Pinterest is currently booming. Their global usage is growing fast for an already large social network. They have $1.7 billion in cash, with little to worry about financially for the next five plus years. Pinterest is likely to get a lot larger yet given their growth rate, they're up to 416 million monthly actives with zero serious threats in terms of competition. Facebook's attempt at building a competitor failed nearly immediately. As with LinkedIn, they occupy a niche in social media that they entirely own.