Sony Xperia Z2 is presented as a flagship fixed term and may be not replaced by a Sony Xperia Z3.
You may have noticed, the gap between the launch of smartphones Xperia Z and Xperia Z1 (January 2013 to September 2013 during CES and IFA) and the one between model outputs Xperia Z1 and Xperia Z2 (September 2013 the IFA and February 2014 during MWC) happened only in few months. According to Yoshiro Kurozumi, interviewed by Japanese media K-Tai.Impress, it will be the same between the Xperia Z2 and its successor.
The product manager at Sony Mobile explains this rate by the need to maintain a flagship to date at a time when mobile technologies are changing very quickly and the desire to offer the best there is to the user. That is why the Xperia Z2 just unveiled at MWC in Barcelona, Spain, will remain for about six months as flagship of the Japanese brand with its Snapdragon 801 platform, with a screen of 5.2 inch Full HD, 20.7 Megapixels camera and waterproof design.
Its successor, for which the Japanese firm has hinted that it is considering a new design and a different name (no Z3 name?), and it should arrive in the third or fourth quarter of the year. At the next event IFA in Berlin, Germany probably?