On February Sony Mobile started a new Xperia line ending the great Xperia Z line. New Xperia Line started with 3 devices which are Xperia X Performance, Xperia XA and Xperia X. So this new rumor says that a new Xperia device join the Xperia X line. This new device will be known as the Xperia X Premium which is a successor to Xperia Z5 Premium. It will have the world first HDR Display of 5.5inches. This also features the Sony's White-magic technology which appeared on Xperia P. This means that actually this display is capable of displaying 1.07 billion colors, compared to the 16.8 million color depth of every other high-end device out there.
Apparently Xperia X premium features 120Hz refresh rate, 2,000:1 contrast ratio, and it will have the brightest display panel ever put into a phone. It will show 1,000 nits of "white brightness" and could actually go up to a maximum 1,300 nits, which is more than twice as much as the 539 nits the Samsung's Galaxy S7 can achieve.
Also Xperia X Premium should be powered with Snapdragon 820 Soc with 3GB of ram. Also rumor suggests that Xperia X Premium will have a USB type C connector. This is still just rumor. Will tell your once this is official.