This is slightly a important topic, however I'm trying to spread the word to possibly start a petition to push for specific updates and content patches.
I think there's a lot we could do.
For example, some ideas that I've been pushing for are custom design pet skins for Ranger and Mechanist, and the application of miniatures to necromancer and elementalist summons.
As well as, "Arcade Map Creator" similar to WC3 or DotA 2 where they have an "Arcade" feature allowing them to have custom made maps and objectives, ranging from fun and comical to monstrous and adventurous.
Also there's a lot of content that you can unlock via the Gem Store by collecting gold and purchasing contracts which can also be beneficial for your "Home Instance".
The "Home Instance" is a pretty large aspect of "End Game Content", because it allows you to consistently collect certain resources required for legendary crafting.