The view from the back would probably be one of the worst in the country.
Yes, it would be. You can extend the kop but you need to stay within design and safety guidelines (which this doesn't).
If you do, you could add about 2,750 seats. Even at that, some parts would be well over Walton Breck Road and you need to deal with property owners, the church, highways, security issues...). You'd also need a new roof (or lift up and extend the old one - it can be done).
On the other hand if Building Control decide that this is effectively new build (which they will), you need to rip out all the existing seats and replace them on wider steps. And you would lose about 2,400 seats.
So for all that pain, grief and money, you'd gain about 350 seats.
You could go the whole hog, push way over Walton Breck Road and build to the absolute maximum with a curved back to the stand to keep within sightline distances and get another 2,150 seats. A total of 2,500 additional seats at a cost of say £70m or over £30k per additional seat for a complete rebuild, some mad cap engineering/civils and a long and protected process to agree with highways etc.