Capacity
With the existing cap on ATMs I think the airport is constrained by a capacity of circa 10m pax. As the new FR deal is projected to increase pax numbers to 5m I can see no capacity issues. Yes the terminal might get crowded and pax might not rate their experience as highly as they do now, but that won't affect the number of pax using SEN. If the flights are there at the right price, the pax will come. After all, just look at Luton, a miserable pax experience but fully utilised by 18m pax.
Hats off to SEN for attracting FR. Fingers crossed it works out for the airport and the wider Group who absolutely need the Aviation division to stop being a drain on Group funds.