I expect that there will be a successor to the S, as it's the volume seller in the K series. Over half of all Ks were the S variant in the UK. In fact, it's sold around 1100 units, versus 1200 for the R1200RT update, though the K has had an extra year on the market.
My guess is that it'll have sharper styling (the C600 Sport looks like an evolution of the K1300S's cues), updated versions of the traction control and electronic suspension systems, more power and better economy. BMW is very big on the latter, so expect improvements. I'd expect platform sharing of a bunch of parts with the revised Rs (not the shaft is now on the same side as the Ks), and possibly engine elements from the K1600 or even S1000RR.
I reckon that a lot depends on where the liquid cooled Boxer comes in. If there's a new R1250S with (say) 150 bhp and a 215 kg wet weight (roughly the same as the old R1200S) then it'd be definitely encroaching on the K1300S's territory. The model line-up might be re-jigged accordingly.
BMW have dropped a lot of hints about a cruiser, and the R platform is considered unsuitable because the cylinders get in the way of a feet forward position. So I think that Dean is on the money as usual.