In my opinion, C-series will be a success from LCY. The SEN catchment I believe will be seriously limited by the impact of development at both LCY (high frequency business) and STN (low frequency LCC)
I do believe that SEN has a c1m market but it will not sustain anything above those levels for long.
The vision of the airport is in conflict with itself. The very reason why a select 'few' choose to fly from SEN from the London area is because it's quiet - therefore the very nature of SEN as an attractive airport must be for it to remain quiet!