I think if AB do fly to LCY it will be using one of there fleet of E190 or DH4. With the E190 being the most likely in my opinion.
If this does happen then I would expect to see AB start flights under codeshare agreement with BACF to BER and MUC and possibly see AB take over the DUS route. This would free up the S2000 to either be returned to T3 or open up another route to somewhere like HAM.