Merchants new to Magento can start immediately on Magento 2.0.
Existing Magento 1.x merchants should weigh their business goals, the benefits of moving to Magento 2.0 (like significantly better performance, scalability, enhanced platform flexibility, and an improved shopping experience), and the availability of key extensions when making their decision.
Magento will continue to support Enterprise Edition 1.13 and 1.14 for 3 years from the Magento 2.0 GA date, so merchants have the flexibility to select an optimal time to upgrade.
When you are ready to migrate, there are data migration and code migration tools available to help you with the process.