There are many underutilized rail corridors in London but getting the province to fund a GO London system is unlikely especially considering that London itself would probably object. This is not due to not wanting the service but rather London would rather have some money for it's planned BRT/LRT system. London, unlike Toronto, doesn't get 100% of it's transit infrastructure paid by Queen's Park.
The 402 northern extension is badly needed in London and would not only get a lot of the transport and regular traffic from Sarnia diverted from the busy 401 but also greatly reduce the amount of traffic the 401 gets from London itself as it would be more convinient for half of all Londoners. London has no intercity freeways so getting from the northern areas of London to the 401 can easily be 30 to 45 minutes in rush hour. Anyone in the northern areas of the city would be in Stratford by the time they even get to the 401, which is exactly what Londoners are doing. It would also relieve traffic on London's busiest road, Wellington, which now carries nearly 50,000 vehicles a day on a regular road with lights and travelling it is a truly torturous affair.
The 402 Northern London bypass is a desperately needed roadway.