Does Seattle have any bus rapid transit lines? I would prefer that to be built instead of more rail construction. They could even run a line along the express lanes of Interstate 5 (or along the express lanes of another highway).
There are two (soon to be four) systems in the region with varying levels of quality. Freeway-based BRT is coming in the form of Stride on I-405 (and SR 522's non-freeway section) by the end of the decade, but it's already overbudget because of WSDOT's demands to rebuild several interchanges.
The express lanes on I-5 would be a poor place for it given that there's already a parallel Link light rail line that is being extended, and that buses would have to deadhead a significant distance in congestion. Prior to the 2021 truncations at Northgate, there were dozens of double-decker and articulated express buses going up and down the I-5 corridor carrying tens of thousands of people. Infinitely expanding buses doesn't really work with our geographic constraints (and importantly, labor costs/availability), so trains are the way to go.
The express buses were, and still are, awesome. I got a job in downtown Seattle in October 2018, and they gave me a benefits card that could either be used to pay for parking or for an ORCA card. I drove the first day, but hated dealing with the traffic so much that I took the bus thereafter until COVID hit. The express buses into Seattle from Lynnwood are very frequent and convenient.
I no longer have that job downtown, but I miss the commute. I like taking transit and trains to get to places when I can, and hate that at my current job in the suburbs, the bus service is so poor (and land use as well, given that I'm in a sprawling warehouse area) that taking the bus takes twice as long as driving when there's traffic. I don't like that I'm essentially forced to drive to work when honestly I'd prefer not to. Now that the light rail has opened to Northgate, I've sworn off driving into downtown Seattle altogether! I still like driving, but only on a rural road or freeway with not much traffic.
I wouldn't mind seeing the I-5 ROW be used for intercity and commuter rail between Seattle and Everett. It would provide a faster way to get between these two cities, since the line along Puget Sound is not centrally located, and that really hampers ridership on Sounder North. (running only 2 trains in the morning and two in the evening doesn't help either) Plus, it would be a dedicated passenger line, so you could run as much passenger train service as you want without having to haggle with BNSF.