Well the A700 is getting on, there are strong rumours of an A500/550 pair that is likely to fill up the space the A700 currently occupies so the only way is up for the A850. So developing my theory of the A850 as an uber APS body to go head to head with the Nikon D400 here's my theory.
Body. About A700 sized, wouldn't be surprised to see more sealing, bigger VF. This seems to be something Sony is staking a claim on. Some small cues to the new 230/330/380 line but not much. Sony will be sticking to the minimalist, little bling look of the A900 at this point. On this point, Sony will stick to CF - justified or not, its the 'serious' choice.
Sensor. I suspect Sony will push the sensor to match the K7/50D so expect something in the 14-16 Mp range. I anticipate that ISO performance will continue to improve but not at the rate some will want. So I reakon we'll get a few more Mp and between half and a full stop better iso performance. Yeah it will still lag the very best in class but so what, it'll still be amazing.
Live View. I believe Sony will give us main sensor LV and will claim that its line about doing it properly applied to getting contrast detect AF working really well in a DSLR. On that point I think Sony will give us a really good LV AF module. Possible - see speed and displays.
Video. I think it'll come with video with a lot of bells and whistles. This is an area Sony should absolutely nail. On a side point, I wouldnt be surprised to see Sony Vegas movie studio shipped with the camera.
Phase Detect AF. This is an interesting one. Part of me would not be surprised to see Sony forgo huge leaps in this form of AF, thinking that we are only a generation from full EVAL cameras and this is a dead end. But while possible I dont think thats where we'll go. AF cross points is the new 'headline' feature - I'm guessing we'll get at least 5, probably 7, possibly 9. I also think we'll see a corresponding increase in 'assist' points. So we'll be looking at something like 20 AF points. All this will come with the usual claims. Again it will trail the Nikons and Canon 1 series but it will be closer than ever before.
Metering. I'd be surprised if there were major changes here. Not a headline feature or a particularly compelling review point. Not saying the current system is great but look at this site, even amongst us geeks its not a topic we give a lot of time to.
Speed. Ok, here it gets exciting (for some). My guess - 10 FPS - why? These things tend to come in round numbers. Data rates simply arent an issue with something like a 15 Mp sensor and state of the art chips.
While unlikely, its possible Sony might feel adventurous and catch us by surprise here. Perhaps a killer contrast detect LV AF, an electronic shutter and an LV 20-30 fps mode.
Controls/displays. Pretty much what we have. Probable. Incremental improvement plus some modification to incorporate video. Possible. Sony must be keen to get an OLED display out there soon, this camera is a likely candidate. Might trade a slightly smaller, tilting OLED for current LCD. OLED tech could also be one of the things that takes LV from toy to truly useful with significantly better angle of view, sunlight and colour performance.
Customisation. Really part of controls I guess. Pretty simple - more. Not as much as the D300 but a lot closer. (yes I realise Nikon will have the D400).
Other bits and pieces. Probable. Frankly I expect in body GPS and some form of wireless data transfer. Lens micro adjust will be there to I suppose. Possible. Some of the stuff appearing on new superzooms like auto panos, face detect, etc
Conclusion. I seriously believe this camera is possible in 2009, whether its possible for Sony is perhaps another question. I think it is but then again I'm used to being disappointed.