Mudchute was indeed initially a siding, but was rebuilt to a platform line when TfL concerns about tipping out terminating trains using sidings were at their height, which made the Crossharbour middle siding in a high frequency service with unstaffed platforms impractical. These sidings don't get used very much, but when they do, such as in disruption, the train can be in them for an extended period.
If you want overprovision of emergency arrangements on the DLR, look at the Beckton line. There a siding at Royal Victoria, a trailing crossover beyond there, a full scissors crossover beyond Custom House, and a facing crossover beyond Prince Regent, all in about a mile of line. Each of these was installed subsequent to the line being built, and each separately needed a full holiday weekend closure, such as over Easter, to introduce. There have been different combinations of using them for extra services to Excel, but now the pattern is to run any enhanced service right through to Beckton.