As a regular user of this line I would say Sandhills is never going to work in handling large football crowds with single 65m units, a narrow platform cluttered with buildings, and a few steel barriers.
Kirkdale can bad enough now and that’s got quite a bit more platform space. Part of the problem like everywhere, is when the ground empties out around 5:00 on Saturdays, northbound trains are already full (often standing) with shoppers returning from town. . I think on match days more services will have to be doubled up/lengthened, as earlier posters have alluded to. The question is obviously how and who will pay.
This overcrowding problem can also occur with Liverpool FC as well, though to a lesser extent.
I think the only realistic solution is longer trains.
Aside I expect the bus companies will struggle too in dealing with the congestion, not forgetting this adjoins a busy route for wagons to the docks at Millers Bridge and Seaforth, and the exit from the tunnel is not far away. Its going to be chaos with a full crowd of 50,000 notwithstanding all the security, stewards and hospitality staff. Yes I agree I don't think this has been thought through.