Opportunity with 5G mobile and wireless communication is 10Gbps data rate possibility while in mobility, where as if we speak about challenges they are many like such as massive MIMO technologies, it will require a mix of new system concepts to boost spectral efficiency, energy efficiency and the network design, green communications, cooperative communications and heterogeneous wireless networks. and more will come up when the actual research will start experimentations.
Yes whenever some new development or concept is about to be thought of one will have the skies in the mind and once the thing starts getting developed the sky starts coming towards earth. :), it's a natural phenomena.
Japan is also after it, along with China and European Commission all are targeting 2020 for 5G implementations. Japan's NTT DoCoMo had announced that it had successfully tested 10 Gbps cellular data speeds last year using an 11 GHz frequency band.
It is right the data limits will be thirsted very soon at high data rates and you will be paying for the auto refreshing advertisements. But by the time 5G will be operational the net access pattern of people will be different. Also the cost of the services will depend how much the multinational are paying for the research and development of the technology.
Clearly, by the time 5G is rolled out, the carriers will have evolved to a different business model or pricing structure for data. Not many consumers will shell out $10 for 1GB (8 gigabits) when they have a 10 GBPS connection. Imagine that, more than ten dollars per second for data charges!