It can kill you! Consider the possibility of a fault on one relay, either a wekded contact holding it closed or a coil fault holding it open. If the other relay switches correctly, a circuit exists via the bulb from the live pin of one plug to the neutral pin of the other. If you then pull out the wrong plug, you've now got mains live via the low resistance of a cold bulb filament on the exposed neutral pin of the plug in your hand.
You'd need to use a single DPDT contactor rather than a relay and it would need to be rated for use in safety isolation applications, i.e. have enough contact clearance and a design that prevents operation of the other pole if one pole's contacts are welded.