"will this route actually make any money" is irrelevant, it's about getting planning permission.
It's that simple.
Agreed - that is a totally different kettle of fish, although of course routes can vanish much more quickly than buildings can. If the new route forms part of a binding Section 106, will this be the first time a commercial UK airport operator has been forced to
add flights, rather than to have a
cap on flights?
Let's also look at it the other way round. Southend to London's an hour by train; crossing London to Euston takes the best part of another hour. People from Essex travelling to The Lake District, Northumberland, and the Cumbria/Lancashire M6 corridor, as well as South West Scotland and the Borders could use this flight and avoid adding to the congestion of London in rush hour.
Yes, of course they could, but the initial question was about whether or not they would, and whether they would do so in enough numbers to sustain the route.
You could apply the same logic to LGW or LTN - each of the "London" airports has its own local catchment area in addition to the parts of London that are near it (including Stratford / Docklands etc for SEN), but the core catchment is still central London.
You might look at INV and say it too has a large catchment around it. However, even with significantly less population than CAX, INV can sustain multiple routes to London because it only has one direct train per day, and is at the end of the route, not a stop which is on the way to somewhere else - infact somewheres elses if we count the daily VT to Waverley - and ditto for why a route to BHX would be unsustainable, given the passing XC rail traffic.
So let's assume there is a binding requirement for the route to operate, and it can even get reasonable loads on some of the weekday morning services, but yields are poor - just as they are if you compare VT prices to Glasgow with those to Manchester.
Do they just continue to run the route at a loss? What if they sell RE? There is always going to be a get out clause.