The number of transactions per second that Bitcoin can handle is limited to 7 per second artificially, and can be changed when needed. Read about it in the white paper - Satoshi was very aware of a figure of 100k per second as being necessary as part of the scale up.
At which point the only people who'll be able to handle the transactions will be colos. Or "Bit-banks" as they'll be known then.
Official "govcoin" is the obvious medium term replacement to Bitcoin, maybe not 3 years, but if Bitcoin doesn't bomb out they will utilise the framework, or maybe even if it does. It could deal with a lot of issues government have if they controlled their own blockchain and it was the primary method of transactions: fraud, tax evasion and money laundering spring to mind. Would be ironic if it became a tool of Big Brother...