None of the US intermountain markets are attractive to the WHL. The Montana markets are small... and while long ago, Billings has been tried before.
Boise is not only too far a drive from the other Northwest cities, but the driving conditions of Cabbage Hill, Meacham, and Ladd Canyon on I-84 will almost certainly cause 1-2 postponements during the average season. I know that the US teams don't like those odds. That didn't stop Boise from nearly purchasing Brandon or Tri-City some 18 years ago... but the league stopped them from buying.
Eugene is the next largest market, but not only does U of Oregon dominate the market, they're not coming up with a hockey arena anytime soon.
Bellingham? I don't see them coming up with an arena.
Wenatchee? They have the arena, just barely, but I'm rather sure the WHL sees them as too small for an American market. Without Seattle and Portland, maybe the league goes there.
Yakima? Sun Dome would have to have an ice plant installed, and the people who control the building have never wanted to do that.
Salem? Again, a building conversion is required and I don't see it happening. Bigger market than you think, though, and really deserves much more consideration.
Bend? No arena, and they've had one on the ballot before. If I had the money, I'd go there; big winter sports market, and really a fun place to both visit and live.