I wonder how much value there is in very fast transport for passengers. If the journey is long enough for high speed to make a difference, you've probably passed through several time zones and the time to reset the body clock will become more important than actual travelling time. I suppose for a quick there and back, staying on place of departure time all the way, would be useful for those occasions when a power handshake is absolutely crucial for a transaction, but that's a case for executive jets, not airliners.