I think Hillsborough could be redeveloped, but we are desperate for some additional space and there's been no facilities plan or major investment since the days of Waddle and Hirst!
We obviously missed the boat on purchasing the land across from the Kop years ago, but it looks like the owner of that land is open to selling or renting out some of it. It would be the perfect opportunity to move the tickets office and shop to here, meaning the current Megast and sports hall could be demolished and space freed up behind the North - maybe for a proper fanzone, extension of the concourse and/or additional turnstyles (removing the ones via Lepps Lane).
The Kop is built into a hill but you could create additional space if it were demolished, flattened and rebuilt.
South Stand just needs some TLC and possibly a bigger flood defence wall. The main issue is the roof which blocks too much sunlight to the pitch.
West Stand is obviously the one that requires the most work. The club would probably need to try and purchase houses on Vere Road (I think they once owned some of these?) to free up space. Liverpool did similar but over a period of many years, knowing that one day they'd develop the Anfield Road stand.