No spec leaked yet, you still can keep up your hope. But I think it's quite highly unlikely for Sony to make a low-res FF sensor. New sensor = new RnD cost, it doesnt make much sense for them to go for lower-res. Remember even at 24mp, the pixel density is merely the same as 12mp aps-c. If the A850 is to be FF (which is again, highly unlikely), it'll use current A900 sensor.
Not necessary... if they keep the same tech as the 24MP sensor and increase pixel size, it won't cost more...