There is room for maybe an extra 8 rows, which works out about 800 seats. I don’t see how this would have much impact on the transport as we hardly ever get 30,000 at the ground anyway.
The main obstacles are if the roof can be held up without the back wall and if we would need extra exits and another concourse. I think there is room for those further back.
Also, I spoke to someone who had worked there during the building and he said the North Stand could be expanded. He might’ve been humouring me, who knows?
If we could add 8 rows, it might look a bit like this:
View attachment 119969
The back wall of the NS is not structural, so wouldn’t prevent your idea.
The roof is held in place by the giant curved trusses, anchored underground in each corner.