Definitely no plans to extend the station building at the moment. The official line on the three barriers is that as people replace their paper season tickets with ones on Oyster, the barriers will be able to handle more people because they go through faster with Oysters. My view is that the whole line has been undersized for the number of people who are using it at present, let alone in the future. The crowding on the escalator at Canada Water is a prime example. Forest Hill Station is one of London's busiest outside zone 1 and yet has only minimal facilites.

Looks like there will be a period whilst the staircases are being replaced when the HOP barriers will be out of use and replaced by temporary validators on the temporary scaffolding staircases.