The Overground Line from Barking to Gospel Oak has been closed for months while the line is being electrified, which will bring it into the same system as the rest of the London Overground. It will add the possibility of four- rather than two-carriage trains and so relieve the crush at busy times. The line through SoTo station has been closed since September, due to re-open in ‘February 2017’ so the end is nigh. To understand why it’s taking so long,. see this article from Rail Engineer magazine, it’s a massive engineering project.