By Maggie Overfelt, CNBC.com
Airbnb is unusual among privately held start-ups in that it's already profitable.
The No. 1 company on the 2017 CNBC Disruptor 50 list has reportedly said it can reach $3 billion in profit by 2020. It was valued at $31 billion last year, meaning that only Marriott's $39 billion valuation is greater in the lodging industry.
But after forcing the biggest changes in travel since Priceline and Expedia, it's running out of easy room to grow against the lodging companies. To keep up its rapid growth, Airbnb needs to upend the entire travel experience.
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