The expansion of the North Satellite for Alaska Airlines, is the only physical expansion that will add additional gates, and only 8 additional gates, and as mentioned previously, it won't be until 2021 when the expansion is complete.
The construction of the new FIS facility will not add any new gates, it will just convert most of the gates on Concourse A into international gates, and relieve the bottleneck of the small antiquated FIS facility in the South Satellite.
Delta is getting two additional gates on Concourse B by converting two wide body gates into four narrowbody gates. There will be a similar "optimization" done on the South Satellite, while maintaining the widebody gate capability.
It will still be many more years afterwards before more gates get added, likely via the construction of a new North Terminal.
So for the foreseeable future, remote stands will be the norm at Sea-Tac, for a number of flights during peak periods. They're almost finished reactivating gate D6, with the construction of an enclosed bus ramp, Concourse B will also have a ground level hold room completed soon for bus operations, and a separate terminal next to Concourse D for hard stand operations is going to be built next year.
There are already three buses, with 10 more on the way, to enable an extensive operation. The Port of Seattle is leasing them all to a new airline managed consortium, called the Seattle-Tacoma Airline Consortium, which will operate and manage all hard stand operations at Sea-Tac.http://www.portseattle.org/ABOUT/COMMIS ... _RM_6e.pdfhttp://www.portseattle.org/ABOUT/COMMIS ... _RM_6a.pdf
"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran