I can't possibly imagine high speed rail connecting airline hubs to most outstations they serve, the costs would be staggering. Paying for right of way, engineering your way through terrain (tunnels, bridges, etc) fighting NIMBYs, building the infrastructure and maintaining it doesn't seem like a profitable business model for anyone not backed up by the endless piggybank of taxpayer dollars.
AMTRAK in the northeast corridor was mentioned before, don't they have to yield the right of way to the freight companies that own the track? They're also never on time.
Positing it would be much easier to maintain an existing airport and service it with RJs. If demand drops, you leave, no catastrophic Big Rail bankruptcies, and a multi-use asset that the community can still profit from.
I'm thinking future technologies in aerospace, avionics and weather forecasting will be able to make up for the shortcomings of regional airline transportation, more so than to step back into the 1800s and "turn it up to 11"