As a concept i attached a screenshot View attachment 22009
we could have it so up to 5 debuffs (or all/select general debuffs) appear above your current target's HP bar
This is not possible. And even if it was would only cause intense amounts of crashing in any fight of scale as it would have to be rendering every set of debuffs on every enemy in render.
As for other skills that apply unique marks above the target already (Such as Stalkers mark) these are unique because otherwise they would overlap making them not recognisable.
On top of having a custom display model that we'd not be able to design more of.
I'm just making a guess maybe those icons are seperate objects in the UI that can be moved to other places on the screen instead of being attached to the hp/mana bar
They're not. They're all 1 fixed together visual.
And even is detaching was possible it would be both buffs and debuffs in 1 detached bar for the current target.