I know this is unrealistic to some but I believe it can be done. The world of Tyria once you hit level 80 gets considerably smaller especially when you get %100 completion.
There is really no point in going back to the lower level zones unless you are doing guild missions.
Everyone wants those tier 5-6 materials and you cannot get them in low-mid level zones. Sure you could mystic forge low tier mats to get better ones but that takes a huge grind and resources.
Southsun Cove is fun and it has an exclusive drop , the karka shell. This IMO is a great idea to continue.
Guild Wars 2 just seems small. Adding a few more zones would fix that.
I would recommend putting more zones near Rata Sum , and the Grove. That area needs higher level zones and it feels like an expansion pack with limited content. There is so much land to the west that could be used.