I wonder what would happen if you had some contact between some group and the Spanish in the 16th century (as early as possible post-Inca), and they somehow received potatoes (and maybe some other crops) from them. Perhaps they could enslave the Spanish and have them grow said crops (while the rest harvest fish and plants in the traditional manner), which would give whichever tribe started it a substantial bounty of food.
Rather far out, but the Maori on the other side of the world received the potato from European travelers a few centuries later.
PNW peoples were sedentary and didn't need better boats, since the land was so rich in food (especially fish). That's probably why they never developed agriculture, because IIRC there's a saying there that you had to be an idiot to starve.
This is the scenario that interests me. What if European colonization had been much more gradual and Indians had time to adapt? Basically the pattern most places was Indians start trading with Europeans, change their society based on new technology, then a generation or two later get wiped out or swept away.
I agree with you that there's not a ton of incentive for PNW natives to farm, but they did a lot of root digging and culturing of edible plants. It wouldn't be a stretch to see potato gardening, since people were sedentary anyway and their food sources were mostly seasonal, though abundant.
The thing PNW natives lacked was an effective store of wealth, hence the potlatch system. What they got from the Hudson Bay Company that revolutionized Salish society was horses, not for hunting buffalo from horseback but as an effective store of wealth. I would have liked to see that last longer than twenty years and see where Salish society would evolve from there.