You don't need a high-speed rail station for that; you just need one of the park-n-ride lots at a light-rail station. You drive to the transit network, then use the local train to reach the regional train.
One of the obvious problems with this, at least in the California metros, is going to be that these stations are watering holes for people who engage in car breakins.
Interesting. I haven't heard of that as a significant problem with the existing Sound Transit park-n-rides; I wonder if that is a regional difference, or whether it is a function of system size.
