Well, seeing the 640 has that kind of specs for that price, there's a good possibility that a 345 would come as the dirt-cheap phone from the range.
About the 1020 successor, if it were up to me, I would rather put the best camera on the current flagship instead of having three separate flagships just to accommodate.
But it's a long shot, though... Possibility is bigger for the 940 using a 20 MP instead of 41 MP.
If they number their phone like this, in my opinion, it's way cleaner than Nokia's numbering as their specs are consistent with the number's tier.
About the SD 820, I think it could come with the 940 XL, but it's a long shot. My guess is it will come with the 950.