High speed rail is only cost-effective between major cities that are within a few hundred miles or so. Otherwise you don't have enough passengers to recoup the cost of building & maintaining the rail system.
For example: Spokane to Seattle is about 230 miles in a straight line, or 280 miles driving. A flight takes less than an hour (not even 40 minutes of which is spent in the air) and costs $80-130 one way. A train traveling 200mph nonstop would take 1 hour 24 minutes. Building high speed rail costs $20-$200 million per mile (the upper end of that is California HSR). If we optimistically assume $20m/mile, constructing the line will cost $5.6b. If all SEA-GEG passengers (677k per year) choose to take rail instead of flying, and we want the project to pay for itself after 50 years, then each ticket will need to cost $165. This also assumes no cost to maintain or operate the rail line.
You sent me down a rabbit hole, thank you, reading about the current state of Cascadia HSR, what it would take to make the current 79mph tracks capable of 110mph or 125mph (spoiler, 110mph is barely worthwhile and 125mph is an overt waste of effort), etc. The more I look at the numbers, the more I think the future does not look like HSR in the PNW. Wildly expensive, low ridership.
I wonder if we could not get most of the benefit by doing substantially cheaper options like separating freight from rail on major routes, electrifying parts of it where feasible. And maybe taking specific segments in areas where the track conditions are already favorable and increasing the maximum speeds on those segments. Probably two-thirds of the route between Portland and Salem, for example, is already suitable with modest upgrades to hit 125 mph. And basically all modern trains are capable of that speed already.