29ers are here to stay .. it's 26" bikes that will soon be extinct.
Look at the US – the market over there is huge and the industry has basically switched to 29ers – 26" is considered 'old news' there – we in the UK are going to "get what we are given" really as it's the big American companies that drive trends and designs in off-the-peg bikes.
IMO – within 5 years 26" designs will be consigned to 'slope-style' and DH bikes… 29ers will be the dominant XC archetype but I expect to see more 650B Full-sus designs developed to offer longer travel AND a larger wheel.