More or less confirmed to 1 VI and 5VI, with the likelyhood being that the 10 VI will follow the same design language:
Mentioned here because the Xperia 10 series have reliably formed the basis of SFOS X devices year on year.
Comment: I think this is a great choice, my favourite form factor to date has been the XA2 Plus with its 6-inch 18:9 screen.
While typing on the 10 III I find it difficult to read this text. Texts in apps and mail are sometimes cropped up. This series is too narrow.
I agree about the XA2 and XA2 plus. Husband doesn’t use the XA2 because the battery dies before noon. My XA2 plus is the best Sailfish phone untill now. Colours are more saturated than on the 10 III. Sound is also better. It’s a bit slower than the 10 III. I have an XA2 plus 32 GB and the cardslot is broken. Not repairable.
It would be nice if Sony’s next step would be: replaceable batteries.
I like the one-handed swipe navigation that the narrow 10iii makes possible, but as someone who uses his phone as a book, i would prefer a wider screen than the current 10 series devices provide.
Let’s hope they do this even before the 2027 EU mandate comes into action.
I think it’s quite easy to change battery at leeast sony xperia 10 lll. My back cover broked and devices quarantee has expired. So I ordered new back cover and change it. Battery is visible when back cover is removed.
Generally speaking it’s more important that the battery isn’t glued to the bottom. I once almost destroyed a friend’s phone trying to change it. The battery shorted and I had to quickly rip it out before it burned the phone.
there are usually special pull-out strings underneath it, and/or you should also use isopropyl alcohol
Those pull-out strings often don’t work as intended and the handle rips off (even said so in youtube-videos describing the process). Isopropyl alcohol helps, but you should use it with caution and as little as possible. I seem to have used a bit to much isopropyl on an Xperia X, and now the backlight is cloudy.
It is doable, but removing the back at first already needs some special tools (A household hair dryer was not doing the trick for me to heat up the adhesive).
If you don’t buy a new back cover, you have to deal with a replacement adhesive seal, which is a bit fiddly to apply.
Was a bit easier on my old Motorola flip-phone, where the battery was simply clipped into the back of the device, and you could carry a spare for quick swap, or get a larger battery with more capacity. 
I really enjoy the 21:9 too with sailfish.
It definitely makes sense to have 19.5:9 for texting and reading, but I’m afraid it won’t feel as comfortable in this case.
We’ll see I guess.