A damn good idea to limit numbers so that there is no-one standing, so booked seats are definitely something to aim for. However, the only practical way it will work is that x number of seats are booked in advance and y number are available for "walk ups" on the day. That way people can still book a seat if their plans change, i.e. cancel their original booking and replace it with an earlier/later train. Of course, it'll need fine tuning and inevitably, some trains won't be full whilst others will be fully booked as no amount of fine tuning will ever be perfect. The important thing is that there'll still be some last-minute availability. Maybe only "open" the last minute ticket sales an hour before departure, so if you are too late, you'd be first in the queue for the next departure ahead of all the other "walk ups" just arriving. We really can't have a situation where you have to book days/weeks in advance and there's no walk up availability - if that ever happens, people will just go by air instead. Trains have the advantage of flexibility and that needs to be ring fenced. But, at the same time, prior bookings must be cancelled and transferred to a different service so that all booked seats are actually taken and used - none of this booking seats and not turning up nonsense.