I think it would be cool to see this route in the game, as this is one of the only commuter rail systems in the PNW. The route There are 2 lines on the sounder the N-line, and the S-line. Implementing both of these would be fairly easy, as neither is very long. The N-line starts at Everett and then calls at Mukilteo and Edmonds before terminating at King St. station in Seattle. The S-line is longer and starts in Seattle then calls at Tukwila, Kent, and Auburn, followed shortly by Sumner and Puyallup. The line then heads west calling at Tacoma Dome and South Tacoma before terminating at Lakewood. Rolling Stock Starting with locomotives, there are two types currently in service. The EMD F59PHI, and the MotivePower MP40PH-3C. It would make more sense to use the EMD F59PHI as it is more common on the network. The locos pull Bombardier BiLevel coaches. On the other end of the train, there are Bombardier BiLevel cab cars. there are two styles of cab cars in use. The originals were delivered when the network was opened and have end gangways. There are also more modern streamlined cab cars delivered from 2017-2022. I feel it would make more sense to add the newer style as the originals are slightly outdated and the new ones look better in general. This is just an opinion of mine and I feel that it is unlikely it would be added.
I'd prefer this to be part of a Cascades/Sounder/BNSF route. The route would include a Cascades SC44 Charger, either the Sounder MP40PH-3C (I'd prefer these, since the MP36s are in game, so this would be easier to add) or F59PHI (both with matching passenger cars/cab cars). As for freight, I'd suggest a BNSF ET44C4/ET44ACH, ES44AC/ES44DC, C44-9W/AC44C4M, or SD75M/SD75I (often seen in Washington on manifests and trash trains), and GP28-2/M/P (rebuilt GP7s/9s/18s), GP39-3 (rebuilt ex-BN GP30s/GP35s; also GP39-2s), GP50/GP25 (rebuilt GP50s), GP60/GP60M(-3)/GP60B, or GP38-2/-3, along with a selection of BNSF rolling stock (preferably different from the Cajon Pass stock, but could also be used on that route).