i live in a place that's not quite as rainy as oregon, but the combination of proper full-coverage fenders and bike paths where i'm not getting splashed by cars means there's only a couple days a year where i'm going to get "soaked" and am going to choose not to ride.
biking in the rain mostly sucks because of splashback from the road. once you've eliminated that, it's no worse than walking in the rain.
I don't think ebikes are replacing walking trips though, but car trips. The requirement to anticipate, prepare for, and endure the weather (including cold, snow, rain) makes bikes much less appealing to people who already own cars, which is almost everyone in the US.
I think the main reasons bikes aren't popular are:
safety (perceived)
weather
cargo capacity
effort requirement
Enthusiasts don't mind the latter and reluctant cyclists will still find sufficient deterrents even if it's eliminated. So I don't think ebikes are really going to move the needle in terms of ridership, regardless of what their buyers tell themselves at time of purchase.
biking in the rain mostly sucks because of splashback from the road. once you've eliminated that, it's no worse than walking in the rain.