Let's put a more positive spin on this.
What kind of Content do you want to see developed?
I mean that seriously. People say there "isn't content", but there is, just not content they particularly enjoy. What kind of content do you want to see?
1. Expansive, Labyrinthine Dungeons?
2. Extremely Difficult Mechanic Heavy Encounters?
3. Randomized, procedural generated content (which Deep Dungeons seem to be)?
What do you think the game is missing, if it's "missing" something? What kind of content would scratch that itch you're having. People say "take risks", but what does that mean?
Some of these seem to be encouraged by the fanbase, while others not. For example, it seems like the player base isn't interested in large, labyrithine dungeons since dungeon delvers go out of their way to skip the few optional rooms we have. Same with exploration, considering how people reduced the (certainly flawed) Diadem into one island. A large portion of the fanbase holds no interest in Savage raids, while others focus on it exclusively. Side content like Lords of Vermillion gets completely ignored quickly enough in favor of more quick dungeon grinds. Players try to DPS or heal past as many mechanics as they can.
What do you as a player want to see developed? Right now for me it's the Deep Dungeons, but what would satisfy you?
I'm certainly excited for the new expansion though. Heavansward was, in many ways, an excellent refinement of what made ARR great. The story was fantastic (leagues above ARR), the dungeons and fights satisfying (especially Ravana and Thordan), and the music phenomenal. I'm guessing that the new expansion will take the game in new directions. It's a common in a lot of games. The first couple of major expansions refine on the core experience, while the others build up new experiences.
To be fair though, the search for the "game with no longevity issues" is the Holy Grail of game design. It's very...very...very difficult.