Why don't trains from Weybridge to Addlestone pull one carriage further forward so station the gates can open sooner and reduce traffic conjestion?
It's an 8 car platform (176m) so it would need a platform extension for 8 car trains which would involve moving a signal and associated track circuiting.
There could be a case for moving the 4 car and 5 car stop marks towards Chertsey to ensure the train stops clear of the detection that the train has cleared the level crossing. After the cost, including signalling testing, then SWR will get the complaints from passengers that they have to walk beyond the canopy when it's raining....
How about moving the 8 car stop marks about one carriage towards Chertsey? I accept it would mean that passengers can't exit from the first carriage (in the same way that they cannot exit from the last carriage at present) but given that (apart from Sunday's and the first train on other days) the passengers can have only got on at Weybridge (where people tend to get on the back of the train given the station layout) I do not see that as an issue.
With regard to your point about people complaining about getting wet - I assume you have never been to Addlestone; the canopy only covers about 3 or 4 carriages at most - it is therefore not going to be an issue!
I have never heard of selective door opening being programmed into any of the rolling stock for the leading coach apart from the Northern Line. Although it's a logical idea, I don't think SWR would be keen on it and no doubt the safety regulators would take years to consider it. A prefab platform extension and moving 1 signal and two track circuit terminations and overlap would be easier....
I used to live near Addlestone many years ago and have used it in the last year, so can visualise the station. It would just be another reason for some people to complain.