Over the years there has been talk of extension to Cranham or one or two extra stations, but now it's timetabled at 9 minutes not 8, there's probably less chance of that unless line speed is increased from 30MPH - whcih it should be - it is ridiculously slow and DMUs used to be quicker.
When I grew up and went to school in the area (1980s), the 'push-pull' (as we called it in DMU days) had a bad reputation for kids leaving objects on the line, and pelting trains with stones from one of the several foot crossings.
I recall the evening service was curtailed because of this anti-social behaviour at one point. I might have mis-remembered, but I'm certain either BR or one of the unions made that threat.
I think the line speed was reduced around that time (late 1980s) after several nasty incidents on the foot crossings. Later (1990s) a friend of a friend was killed at Emerson Park, messing about on the station roof.
At one point, there were proposals for a new halt at Wingletye Lane, which would have served the new 6th Form College. It came to nothing.
I re-visited the line a couple of years ago, to travel 'first class' in a 317. One of the driving coaches - furthest from the exits at both Upminster and Romford - was being used as a mobile youth club by local kids. Clearly, not much has changed in my absence!