Magento 2 had a slow birth. After being first announced in 2010, and with a planned release dates for 2011, it eventually emerged as a beta version in the summer of 2015. This new version of Magento was a major update with much of the underlying technology changed or updated. This allowed the platform to overcome many of the performance challenges of the first version, but at the cost that theme and code customisations, including 3rd party transactions are not transferable, requiring a code re-write for Magento 2. There are also some horror stories of the challenges of data migration for some of the early adopters.
Move onto 2018 and Magento 2 is a much more mature system with major performance improvements over Magento 1, and is now gaining market share again over many of its competitors. A wide range of Magento 2 extensions are now available. In number less than for Magento 1, but in quality far better. With the launch of the Magento 2 Data Migration Tool, there is now an efficient and reliable method for the transfer of your products, customers and order data, store configurations, promotions and more to Magento 2.
Magento 2 is now a stable and proven ecommerce solution that offers substantial performance improvements over Magento 1. Magento 1 publisher support will not continue forever; originally expected to cease in November 2018, Magento Inc have since made a commitment of a 18-month notice prior to the cessation of support.
2018 is the perfect time to upgrade your existing site. Magento 2 is a mature product. The inevitable rush to migrate (and the resulting shortage of development resource) in those last 18 months prior to the cessation of support is still ahead of us.