I think that the larger "hub" airports will be fine. They have a captive market and are able to "sweat their assets" as the troughs between peaks fill up. Overall revenue is up - its just not increasing as fast as passenger numbers. You will no longer have nice empty surroundings like you did in earlier years of aviation but that's a price of cheaper fares.
The problem is the smaller airports relying on fickle LCCs (possibly Irish based). I remember over a decade ago a knowledgable person predicting that Ryanair's growth would be limited by the ability of airports to subsidise them. He was wrong in this case (so far) but I wouldn't want to be manager of such an airport. Have a look at the thread on half of airports not having a water fountain. They are trying to make money with car set down charges, selling bottled water and other goods at stupid prices, offering expedited security for a fee so you catch your flight, etc because the landing fees are so low. That irks people off and is not good in the long term. (Parallel with BA?)
Heathrow may be a special case in that it is regulated and can raise prices for existing passengers who will efectively be cross-subsidising future travellers (a bit like London rail commuters) - an airline couldn't get away with this. Presumably that was the case for ZRH, FRA and other "hub" airports that have built new facilities.
If you look at "Boris Island" (ok the only way it will ever get built is if Mr Johnson becomes PM) the cost is quoted as £50 bn. I don't know the assumed cost of capital - it could probably be financed using cheaper debt rather than more expensive equity financing but I am certainly not the expert - but lets assume that depreciation and finance cost is £5bn p.a. Lets say that it has 100m passengers p.a. That would cost the passenger £100 per round trip. Hmm - doesn't look great to me.