I think you're mistaken to say that PAE will be another BLI for Alaska.  I currently commute weekly into/out of BLI (for my work in Everett).  However, most of my co-workers think I'm crazy to drive to BLI.  Upon hearing of Alaska's PAE service, most said they'd definitely fly out of PAE.
If you look at what Alaska is spending expanding SEA's North Terminal, you'll see they have a significant financial incentive to fully support expansion of flights into/out of PAE.