you could put a camera on each carriage to ensure better vision than the guard can have, and have a procedure that you cant power up until doors are closed. i have more faith in the ability of drivers to check a camera, see no one is there, shut the door, check doors shut, then engage the accelerator than other here seem to have. they seem to operate the rest of the train safely enough.
Theres is already a camera on each carriage and already you can't take power without doors (in theory ) being closed. The point again being that the cameras can't see anyone running for the train and it's very difficult to see if anything small such as child has fallen between train and platform. Not to mention the fact that the driver needs to be concentrating on driving the train safely not scanning up and down a line of 12 or more cameras. Very easy to be so concentrating on ensuring everyone is safely onboard and then go straight through a red signal. A human halfway down the train who can scan the full area, speak or shout at the passengers and can hear any commotion going on has to be the best way of safely dispatching a train and even then I would argue that the gradual removal of platform staff from stations over the years has made even this less safe.