Developers could create dungeons that scale infinitely with players, but it poses a lot of problems. Skyrim / Elder Scrolls attempted scaling, but it caused issues with certain strategies becoming outdated as there was an inherent expectation the player would grow their character a certain way. Additionally, there is the problem if getting used to playing FFXIV again after taking a long break and then not remembering how to play a job. Scaling down removes late game abilities and makes the rotation simpler, so people can relearn jobs doing old content.

TLDR the best you can hope for on scaling is the Unreal Trials. I wouldn't expect much more.