Fel scared for havoc/vengeance aldratchi for vengeance/new spec
Blade dance focused hero talent for havoc/new spec
New spec focused on under utilized or removed dh abilities, old style moment, fury of the illidari, glaive throws legendary from shadowlands, chaos blades and most importantly a spec that doesn't have a demon form to help deliver the actual dh fantasy of fighting demons and actually resisting the demon within rather than being like "erm yeah you can have control as much as possible actually"
Other mechanically hooks would be built around glaive work combos and bleeds, giving the new spec deflecting dance with two charges of blade dance would allow it to be an actual defensive and allow havoc to get an actually defensive as well instead of weak ass blur
Make it void themed, give us void elf demon hunters, allows the eternal havoc mover debate to end restored the lost early legion play style and even allows havoc to have a functional tree and be freed from 36 button opener