A new rumor suggests that a follow up to the Xperia Z5 Premium will be at Mobile World Congress at the end of this month, although it also suggests that it won't be shown off in an official announcement and will instead be unveiled in private with select individuals, which could likely be those who are set up for briefings with the company as these types of meetings can happen with just one or two people. The details come from a tweet sent out earlier this afternoon stating that a Sony Premium flagship is coming and will be shown off at Mobile World Congress in "secret rooms."
While there is no way to validate this rumor, a situation like this wouldn't be completely unheard of. It's also possible that Sony's upcoming device that is known as "Yoshino" may be the successor that this rumor is referring to, as this particular device has been said to carry some top-tier specifications including Qualcomm's upcoming Snapdragon 835 processor, and a 4K display that may be akin to the technology used on the Xperia Z5 Premium, which would only activate in 4K resolution for the user when they were viewing 4K content and the rest of the time would fall back to Full HD like every other Sony flagship for the last few years.
A recent rumor suggested that the Yoshino device would be launched at Mobile World Congress this month, but it may not actually launch due to the use of the Snapdragon 835 processor, a chip that Samsung is also said to be using in their upcoming Galaxy S8 which is rumored to have exclusivity on the use of this processor until after the phone launches. This might be a reason for Sony holding off on officially announcing their 2017 flagship device as they likely don't want to be forced to use the older Snapdragon 821 CPU, which is what LG is reportedly doing with the G6 that is also to be announced at the event in the next weeks. Even without a flagship announcement at the event, Sony still has other devices that are expected to be announced, so there is still something for Sony fans to be excited about.