I'd like to go back to the original leak text and try to extrapolate from the exact words of the original poster.
"This is a result of Network turning their efforts to "focus" cities. These are cities that are underserved and are not a hub for competitors. The model for DL was RDU. In short order, we add ~20 non-stops per peak day (often only 1 flight to many hubs) and a transatlantic flight to CDG, AMS or LHR.
The first thing that jumps out at me is that this requires very, very little in the way of CapEx on DL's part. It's not routing connections through any of these cities, since all or almost all of the flights are to its own hubs. This means that, barring some truly unfortunate timing w/r/t flying times and banks at hubs, they can continuously flow through a small number of gates at the focus city airport. And 20 flights per day just isn't much, so you might not have much of a fixed base in terms of crew or TechOps, although that's not a certainty, and this is Delta and they do weird things in both of those categories.
Even with one flight a day to each of its hubs, DL is suddenly in a much better advertising position to sell corporate contracts to local businesses: "Hey, wouldn't you like to fly with the airline that is flying nonstop TATL and
to NYC and
SEA?" Actually flying all those routes to all those cities might be a little expensive, but it wouldn't surprise me to find out that DL has, or thinks it has, a structural advantage on CASM for both personnel (non-unionized labor) and fuel (the couple of basis points per gallon it gets from the Trainer refinery, not just directly from crack spread but also the insider knowledge it gets for negotiating with suppliers elsewhere).
Airport managers are going to love those new nonstops, especially TATL in markets that don't have a TATL nonstop yet. DL can expect to be greeted with open checkbooks. In cities where those incentives come with a exclusivity clause, it also shuts out competitors from picking up that money.
It's not just the power of the nonstops, though. Flying to (nearly) all of its own hubs, including one of CDG, AMS or LHR, means that the focus cities are now one stop away from anywhere
DL and AF/KL or VS fly. Maybe Y passengers will only care about price, but premium cabin fliers are going to be looking for comfort and faster trip times. Hold that thought.
Where is DL going to implement this focus city strategy? RDU is the model. So we're mostly looking at mid-market cities. The Midwest has been brought up a lot: we can safely assume IND, but also frequently mentioned in this thread and elsewhere are MKE, CLE, and CMH. To that list, perhaps add STL and PIT. Elsewhere in the country, AUS, and maybe MCO. Cities where AA and UA aren't going to sink enormous amounts of resources to defend; they're not capable of supporting a full hub on their own, so the US3 have abandoned large segments of market share to WN and the LCCs. Remember all those premium cabin flyers looking for the best network for corporate contracts? Where else are they going to go? WN doesn't fly to Europe. AA and UA will fly nonstop to their own hubs in NYC/LAX/ORD, but for non-hub flights (especially secondary European destinations) they might well only be able to offer a two stop flight. And yes, between AA and UA, they have hubs in all of the top 10 metropolitan areas, but corporate customers are going to be looking to fly to AA hubs on UA contracts and vice versa. It's a tight bind, and while no single city is worth the resources to get into a slugging match, letting DL sweep up all the high-value traffic in market after market is going to hurt yields network-wide. There are some countermeasures, like building up those secondary routes in Europe through PHL and EWR, but that's very
expensive in the short term.
The big question mark is where DL is going to find the TATL demand to fill all those new flights. It doesn't have anything smaller than a 763 on hand for these mission lengths, and the precedents of IND (propped up by GE Aviation air freight) and CVG (propped up by GE Aviation air freight AND a big contract from Procter and Gamble) don't bode well for load factors. Also, where is DL getting its hands on so many 763s (and/or 764s)? And how long does it expect to keep flying them? A330s might be longer for this world, but they have even more seats to fill. Perhaps a 752 can squeeze out a flight from MKE, CLE, or PIT to LHR, but LHR has by far the worst onward connectivity of DL's 3 European hubs, and the same question of "where do you get the 752s and how do you keep them flying" still applies. CDG is also just a friendlier environment for expansion, from a technical feasibility standpoint; far less restricted than either LHR or AMS. A321LRs don't help, they don't have the range. Boeing MoM might be an ideal plane but is too far over the horizon.
To summarize: I think DL is leveraging certain structural advantages it has to attack both WN's p2p network overall, and AA and UA's hub-and-spoke networks from the biggest and least defensible spokes. It's an interesting gambit, only possible because of idiosyncrasies at DL, and because they are sufficiently flush with cash that they can take risks. It is not something that DL's competitors can imitate; they must counterattack asymmetrically in order to maintain position.