Next Sony Mobile flagship: What's the story on the next Sony Xperia?

With Sony's naming convention changing drastically in the last few years, it's difficult to pick apart exactly where it might go next with its smartphones.
Having ditched the Xperia Z naming, we're expecting some action in the XZ family. Currently we have the XZ Premium, XZ1 and XZ1 Compact which really sit in the flagship space.
There are rumours of a range of incoming Sony Mobile devices, so here we're picking apart the rumours to bring you the details on what we expect next in the Xperia flagship space.
Next Sony Xperia: The name

The Xperia XZ Premium appeared in early-2017 as a loose replacement for the Z5 Premium, defined by the 4K display and otherwise flagship specs. It wasn't until August 2017 that the Xperia XZ1 appeared, sitting in Sony's conventional flagship space, with a Full HD display and again offering Flagship specs.
The next device launch from Sony might be a new Premium device which would technically be due for an update, as the XZ1 is only 6-months old, but that hasn't stopped Sony before.
At the time of writing there are a lot of Sony Mobile devices that might potentially appear, all disclosed by UAProf (user-agent profiles), with some spec sheets appearing carrying Sony product numbers, but no indicator to real product names - but it looks like there's a new Premium model and a new XZ1 replacement, and probably a whole collection of variants and mid-range models too.
Next Sony Xperia: Design

Sony wants to change the design
Slimmer bezels expected
Increased screen-to-body ratio
IP65/68 expected
Sony Mobile has been using the OmniBalance design since the launch of the original Xperia Z and through into the X family. It has changed incrementally over the years, but on the whole, Xperia brand design has been fairly consistent with the occasional change to devices like the Sony Xperia XA with its really slim bezels.
In September, The Indian Express reported that Sony Mobile plans to change the design, quoting Sony India's managing director Kenichiro Hibi saying: "…we are planning to launch new generation of products and you can expect a complete new design from the devices."
Exactly how "new" this design will be remains to be seen, but leaked specs that have appeared so far don't seem to suggest a move to an 18:9 display, even if a purported design leak does. There's little else that suggests this change, but while the entire display appears to be dark, it might be that the bottom section isn't active display and is just there's the touch controls sit. Looking at the Xperia XZ1, there's a lot in common, however, especially around the right-hand buttons.
Elsewhere, the appearance of a device called H8541 with a spec sheet, however, suggests a big screen phone with a body that's smaller than the XZ Premium, which might represent this change in design. Reddit user Piastavgo created some mockups of this potential layout, picked up by XperiaBlog, to show what it might look like, based on leaked dimensions

Leaked specs have mentioned IP65/68, so we'd expect waterproofing, which any self-respecting 2018 flagship should have.
Reliable leaks are rather scarce at the moment, but we suspect we'll soon start seeing much more appearing in the rumour mill.
Next Sony Xperia: Display

H8541: 5.7-inch 4K display mentioned
H8216: 5.48-inch Full HD display mentioned
We've mentioned that leaked specs don't seem to reflect a shift to an 18:9 display and that's because reported resolutions stick to a 16:9 aspect instead.
One of the first leaks was for a H8116, which reported a 3840 x 2160 pixels for the display, or 4K. That would make it an Xperia Premium model, but we've heard little else about this model.
There's also the H8541, again with a 3840 x 2160 display, but with a complete spec sheet attached - as we mentioned above - reporting a 5.7-inch display. That's pretty big for a 16:9 device, growing larger than the XZ Premium, which might work with a slimmed down body. More on this phone below, but that's the device suggested to have a redesign as above.
We also have a reported device known as H8216 again with a spec sheet attached, returning to 1920 x 1080 pixels and with a 5.48-inch design. This phone is interesting, because the specs suggest that display is crammed into a body similar in size to the current Xperia XZ1, suggesting a bit of a design revision again, as detailed above.
In all cases, we're expecting Sony to stick to using LCD panels, preferring the Triluminos display with X-Reality, over OLED. We'd also expect HDR, as in the XZ Premium and XZ1.

Next Sony Xperia: Hardware specs
Mixture of SD835 and SD845 devices reported
With the positioning of future Xperia handsets not being entirely clear at the moment, there's a mixture of specs being touted. With lots of model numbers in isolation with few other details, the strongest leads we currently have are for that H8541 (the Premium update?) and H8216 (an XZ1 update?).
The H8541 appeared with a leaked spec sheet suggesting a Qualcomm Snapdragon 835, 4GB RAM, 64GB of storage. There's USB Type-C, a 3420mAh battery mentioned, with Quick Charge 3.
For a new phone, it's perhaps surprising that it might be running on 2017's flagship hardware, with Snapdragon 845 expected to appear in phones in early 2018.
This, perhaps, suggests that this device might never launch - but then Sony has been rather random at times - but if this is an exercise in revealing a new design, then perhaps it will get an early-2018 launch.
The next device is the H8216. The leaked spec sheet suggests a Qualcomm Snapdragon 845, 4GB RAM and 64GB storage with microSD. There's mention of Quick Charge and a 3130mAh battery.
Again, there's very little information to go on at the moment, so this is far from final.
Next Sony Xperia:
Cameras
With things not being very clear so far on Sony's plans - and exactly how these two devices align - there's something a lot more interesting lurking in the leaked specs for that cameras.
Starting with that big screen 4K phone, there are no details shared about what camera it might be equipped with.
So we'll move on to that H8216. The camera details here are a lot more specific, suggesting twin 12-megapixel rear cameras and a 15-megapixel front camera.
Of course, the source of this information is in Chinese, so there's every chance that it's the other way around. We're sure there will be a lot more chatter, but we could be looking at Sony's first dual-camera smartphone for 2018.
Next Sony Xperia: Release dates

CES has been used before
MWC almost a certainty
Apart from 2018 dates, there's been no real confirmation of when we might see any new Sony Mobile phones launched
. Sony has used CES - in January - to launch mobile devices before, but we're much more convinced that Mobile World Congress, in February/March 2018 will see the launch of at least one new device.
At the moment it's difficult to discern exactly what device that might be, but we'll continue to sift and report on the leaks and rumours that might provide some insight.