Preview at WWDC likely in June, followed by September launch.
Intel Announces Next Version of Thunderbolt With 20Gbps Throughput Coming in 2014
The new generation of Thunderbolt, code-named 'Falcon Ridge', will be backwards compatible with current-generation cables and connectors. Intel expects production to ramp up in 2014.
An on-stage demo with fresh-off-the-press silicon showed the new Thunderbolt running 1,200 [MB/sec], which is certainly a step up from what's currently on the market.
A minor update to Thunderbolt, called 'Redwood Ridge', will be included in some of Intel's upcoming 'Haswell' Core processors.