The issue is how many people are actually going to take the train? In order to get around anywhere other than San Francisco, you need a car.
I'm from the Bay Area, so let's use going down to LA as an example. Sure I take the train, but I need to drive everywhere else once I get there. Why would I bother with an expensive@$$ train ticket when I can just drive?
Before you argue that this is going to kill the airlines and pull flight data from SFO to LAX and vice versa, remember that SFO and LAX are United hubs. SFO is the UA gateway hub to Asia, meaning a lot of people fly from LAX to SFO to connect onwards to NRT, TPE, PVG, PEK, HKG, ICN, etc. Similarly, LAX is a hub to Latin America and also has a decent number of flights to Asia (5x flights per day to NRT, 5x to TPE). And honestly, what are you really solving? I still need to drive my ass to the train station and park there. Might as well just fly, because if you fly the regional airports (i.e. OAK to SNA), you're there in an hour, and we all know how regional airports = short security lines. My point is a lot of that air traffic is going to continue because there's a lot of hub traffic.
I'm not against public transportation. I travel everywhere in Asia, and compared to Asia, the US (even NYC) is a 3rd world country in terms of public transit. The new clean subway systems in Chinese cities put America to shame. Even the older systems like in Tokyo, Seoul, Hong Kong are way ahead of what you have in NYC. Just taking the BART to SF makes me want to puke with those fabric seats and 1970s rolling stock.
If anything, I think we'd be better off rolling out heavy/medium rail further in the SF Bay Area or LA area to help with highway congestion. HSR just makes more sense in a more populated area like the NE corridor. It works wonders in Japan, and even highly populated areas like Taiwan are showing huge struggles to maintain HSR operations.
Final question: What are the prices going to be? Amtrak is currently $58. Why would I pay $58 when I can easily get a $99 Southwest ticket and possibly even lower prices? How does HSR plan on fitting itself in there? If it sits between $58 and $99, say $75, that could be cool to try it out, but really why would I pay that again?