I've read that they are interested. It would extend Idaho to the Pacific Ocean and give them a seaport in Coos Bay, if certain adjoining counties in the proposal join.
Idaho has a "seaport" already, in Lewiston (across the border from Clarkston WA). You get there by way of the Columbia River and locks. I often haul giant rolls of paper in my semi from the papermill in Lewiston.
Also by way of the Snake river (which gets to the Columbia just before the tri cities). The snake river goes all the Jackson hole, but isn’t navigable for most of that (well, those parts are very good for white water rafting).
That implies that Idaho has the money to build a deepwater port and connecting infrastructure that currently doesn’t exist. And there’s not really any particular benefit since there is free movement of goods in the US; customs fees are not a state level thing to begin with.