I don't believe I ever said that DL would or could turn SEA into a full-fledged hub on the scale of JFK. But DL clearly has had plenty of success in adding new flights, both domestically and internationally including in markets like LAX-SEA where DL operated multiple mainline domestic flights even where those flights didn't connect with DL international flights - and the flights were full. Now, we all know that full flights don't equate to profitable flights but given that pricing is strong in the US and SEA has good pricing thanks to AS' hub, it is likely not hard for DL grow. The 717 is physically not that larger than an E170/175 which DL is using in SEA but the 717 carries more people. DL also has the ability to upgrade existing mainline flights such as on the 738 to the new 739s. DL does have options to grow SEA.
I didn't both that DL is trying to fully replicate everything AS does but they do intend to have a presence in the top markets and perhaps add more flights beyond there. I don't know all of the ins and outs of the physical operation at SEA, but it isn't beyond the realm of possibility that DL is working with SEA to create more capacity, possibly including a remote RJ operation; those types of things exist at other airports. If DL has determined it needs to grow SEA and the port wants DL's growth, there will be solutions found to make that happen. Even if DL is nearing its capacity short-term, SEA will find ways to accommodate DL longer term.
Keep in mind that even though AS has multiples more flights than DL, DL still is the solid #2 at SEA and carries 70% of AS' revenue because of the value of the int'l flights. DL is not the also ran in SEA that some would like to think.
I have no idea what is behind the falling out between AS and DL but DL clearly wants an exclusive relationship with AS and AS is also running high enough load factors on its own flights that DL cannot get the seats on AS that DL needs to feed its int'l flights and it shouldn't be a surprise that DL is turning to another plan to ensure its int'l flights are properly fed.
DL's latest move seems to say that intend to vigorously compete in the largest SEA domestic markets.
http://finance.yahoo.com/news/delta-offers-double-miles-seattle-150000949.html
As for the impact that AS' ending of ground handling with DL would have, AS' service in most cities east of the Rockies is 2 flights per day. DL is adding that much capacity or more in most of those cities because industry capacity is rising again because AA and US are doing so in order to increase their own network footprint. Some of the cities that AS serves such as ATL and MSP probably wouldn't work for AS without DL feed at DL's hubs.
DL has made it clear that SEA will be a major city in DL's network going forward. The 767 and 330 are not traditional transpac aircraft but DL is successfully using them to open markets in the same way that CO used the 757 to quickly build a transatlantic network at EWR at costs that allow DL to very effectively compete with other carriers. DL also has strong partners in China and Korea (DL still codeshares beyond ICN on KE) as well as its own operation in Japan which isn't going away.
The other part of this puzzle is that DL and AS share gates at LAX yet DL has preferential use agreements over AS for some of those gates because DL helped pay for part of the remodeling of T6 at LAX. DL has the ability to significantly hurt AS at LAX if the two of them can't resolve the issues or if DL decides it needs to grow LAX on its own.
DL people are benefitting from DL's growth at SEA and there will be more.
