Strange because the DLR is almost completely automated (no driver, but ticket inspector closes the doors) and has no platform edge doors. But they do have emergency stop buttons on the platforms.
> allows the conductor to take control in the case of a
> complete (or widespread) signalling failure
Most automatic trains can't be driven by humans under normal circumstances because signaling information is fed to the train far faster than any human could react to it.
(The Central, Jubilee, Northern and Victoria lines also use automatic operation to similar levels as the DLR, it's just less obvious as the train operator still has a separate cab).
There is no such need. Lyon's line D has been running fully automatic since 1992 without platform doors[0], the only major accident has been a drunk falling on the train having jumped from a mezzanine.