Even the fastest passenger trains are quite slow compared to average airliners, and there's a lot of places connected by air that don't have train tracks between them. Air travel should stay dominant until both of those things change.
Only beyond a certain distance — there are a few routes in China and Europe where the train will get you from A to B faster than an aircraft due to the aircraft's speed advantage mostly being in cruise flight. If you take into account the time spent in the airport at either side, there are actually a lot of such routes.
