Satoshi said, by 2020 bitcoin is eitheir mainstream either will disappear (quotation welcome, i didn't find it)
But how can it be mainstream with 7 transaction per second ? And if it's not mainstream, satoshi's logic woul tell us that
bitcoin will disappear by 2020 
In few more years who knows we might probably found a solution to solve the scalability issue and have the network being able to handle higher number of transactions than currently. Anyway, when he quoted saying that in 20 years there will either be very large (bitcoin) transaction volume or no volume, that was actually made in 2010, so theoretically, we have about another 15 more years before we get there.