I think domestic P2P platforms are a big untapped opportunity in developing countries, especially large ones. They are still rare; Fairplace in Brazil is a notable exception.

An international platform like Zidisha can offer a different value proposition, in that 1) we enable arbitrage in purchasing power parity between wealthy and developing countries (the price of dinner at an upscale restaurant in America could finance the startup of an entire restaurant in Kenya), and 2) our users value the chance to connect with an ordinary person on the other side of the world, learning about their culture, socioeconomic realities, etc.