Tali and I went to Climate cam in Yorkshire last week. By car. Ironic considering the nature of the event. We would have loved to take the train and taken bikes with us but the train operators policy seems to run along the lines of "book well in advance and you might be able to bring a bicycle assuming no more than a couple of others want to do the same".
The old style trains often had a guards van suitable for oversize luggage, smoking and other uses. New trains have no equivalent. I cant imagine that the marginal costs (rolling stock, and energy chiefly) of hitching another nearly empty carriage, with either bicycle racks or even just metal bars to lock on to would be prohibitive. Doing so could make train travel a lot easier and pleasurable.