Panthers Stadium is now probably the best single-use club ground in Sydney. Just continue to do minor upgrades to it, and a 10/2 split or 9/3 split where the Panthers play their derbys at BankWest is probably what will happen going forward.
Realistically, Manly or the Saints would kill for a stadium as good as Panthers is now at Brookvale or Kogarah.
Penrith is the only one of the Sydney suburban grounds I see with a real future. Decent now and the Leagues club has endless cash to splash, they could realistically afford to upgrade it.
Maybe Campbeltown Sports, with the new A League team giving it a good chance of quality upgrades.
Kogarah, Brookvale, Shark Park, Leichhardt. Single club parks, very little financial backing from owners and/or councils. Their use in first grade will decline over the coming years.