Everyone can add in below in comments, the functionality they would like to see in the next Xperia flagship.

I've compiled a list below and hope to see Sony leverage its capabilities to bring the best in the Xperia 1 IV next year. Although I do like Sony's approach in focusing on; Audio, Gaming, Photography, Cinematography, Cinephiles & Performance, there is still a lot more that Sony can do in this space.

This is the list of features I would like to see:

1) Better Selfie Camera- using Sony's own IMX sensor, larger sensor size, higher MP & support 4K 60fps video.

2) Include tech from Bravia XR, so utilise some form of cognitive intelligence, add in some of the features such as:

XR OLED Contrast Pro, XR Color, XR Clarity, XR Motion, Dolby Vision/ HDR10+ Support etc for mobile. It will not affect TV sales due to screen size difference and TV's have different purposes- Samsung is a good example of this- in fact, they optimise sharing features etc exclusive to Samsung smartphones for higher quality video/ content transfer and having a better display on smartphones encourages more people to get TV's from that brand if they like the smartphone.  

3) Leverage Bravia x Sony Pictures so we can get something like Bravia Core for mobile (4K content on mobile is currently too limited, Prime is temperamental as not all 4K content is available in 4K on mobile, Netflix is capped at 1080p, Disney+ is capped at 1080p etc). 

4) Improved Camera performance working with Zeiss and Alpha division- especially video, we definitely need an automatic mode in Cinema Pro, better dynamic range, multi-exposure framing for video, better stabilisation, higher bit-rate video, 8K, oversampling to get 4K video using full sensor size, more aspect ratio options e.g. 16:9/ 17:9 video in Cinema Pro, S-Cinetone, possibly Dolby Vision, 4D Focus, time-lapse, better video in the native camera app similar to the basic mode for photo pro. In general larger MP and sensor sizes across the board. If Sony wants to stay competitive they need to be better than competition smartphones, they need to realize that making an amazing smartphone camera will not cannibalize/ harm professional camera or DSLR sales- but if you put poor performance cameras on your smartphones, people will just buy smartphones from other companies such as Samsung or Oneplus and that drives revenue away from Sony. 

5) Add in more modern solutions and features such as reverse wireless charging, Night Mode Photography and Cinematography, 12-bit photography, 8K video, larger battery sizes, zoom capabilities, better 5G and mm wave support, new display tech (better/ brighter panel, higher res 5120*2160 etc).

6) Gaming should incorporate PlayStation Division- exclusive PlayStation games for mobile but only available on Xperia smartphones, PS Now in 1080p/4K, PS5 Controller Support, PS5 Remote Play, etc.

7) Better Software- move away from stock android and make software more stable, there are always problems with late rollout of android and there are always issues on older devices. Sony needs to fix this, bring back stuff like the gallery app, increase software support time for devices and make sure apps such as the native camera app, cinema-pro and photo-pro do not crash and allow photography and video-recording below 5% battery, as there are moments that are more important than battery life that once missed can not be retaken.