First off, I would LOVE to see Home Instances have more customization, alongside a second version you can go to that is either in an expansion map, or Living World map (IE. a Grothmar Valley home instance or a Rata Novus one), to elaborate on the customization side of this, here is what I would like to see:
Placement of nodes and Personal Story characters being able to be changed
Choice-based decorations (like replacing the Blood and Ash legion things with Iron Legion ones, and vice versa, or having the Diessa Chalice be placed on a pedestal)
Change the kind of NPC in the instance and being able to change them to different versions based on your preference
The ability to have your toons roam in the instance, talking to them would let you change them without needing to log off (maaaaybe this would be QoL)
Second, Professions, everyone would LOVE to customize their profession effects, and here are some ideas I and some other people have
Changing VFX color (IE. Foefire blue Elementalist fire, or red mist-smoke for Revenants)
Changing the theme of your profession skills (replacing butterflies for Mesmers, or changing the Jade Mech)
Profession Weapon Skins (Gunsaber, Reaper's Shroud Scythe, Photon Forge Weapons)
Now, for the one I would LOVE to see; Legendary Weapon Skins
Yes, this seems like a stupid idea, but the Aurene Weapons had the Elder Dragon variants just fine, so why can't the other legendaries have their own variants? Here are my ideas:
Exspiravit (Revenant-themed Exordium skin)
Vlast's Voltage (basically with Vlast instead of a random dragon no one heard of, and is a Khopesh)
Flames of the Forge (a Forged version of the Flames of War
The Giver (for the Juggernaut, basically replacing Atlas with Prometheus, and the hammer being themed off of molten iron
Adelbern's Gavel (For Sharur, making the Orrian Theme replaced with an Ascalonian one)