Just a PDX pax here, but my two cents is HA won't be impacted by SWA as much as the other Airlines will...
1) Hawaii is much more of 'premium' destination than most of the leisure destinations SWA flies to. It's more like the Virgin Islands / Turks & Caicos, than it is Mexico or Florida.
It's the lodging, food, drinks, and recreation in Hawaii that's actually super expensive. I'm much more worried about how much the 6-Nights + $25 Drinks/Sandwiches at the resort are going to set me back. The flights are a smaller % of the total trip cost vs a trip to Cabo or Puerto Vallarta.
Spending a few extra $ to take Hawaiian is not a big deal for people that can afford Hawaii.
2) On a 5-6 hour flight, most experienced flyers will consider Aircraft & IFE much more. The choices for me (in order of preference) are:
Nonstop: HA A330 (rare sighting these days) or HA A321
Nonstop: AS 737
1-Stop: Delta through SEA
1-Stop: UA/AA
For this reason, I think SWA will hurt AS/AA/UA much more than it will HA.