lotus staves are available with most attributes, so you actually can get them easily.
There are other skins that you just can't get unless you unlock the pvp skin and transfer it to a bonus weapon.
a nice skin that immediately comes to mind for me is canthan short sword, which is only available as a green (law and order) that isn't even a sword.
I’d love to see some new armor sets like the Warmaster Grast version of Templar armor. Could add a lot of interest.
Adding on to what Danthor said. I would love to see Eternal Warrior Platemail to complete the Ghostly Hero look without tonic.
Edit: Adding a link to the armor for visibility.
Speaking of the eternal it would be awesome if they added the option to craft an Eternal Blade at the Eternal Weaponsmith in FoW.
Labyrinthine Spire comes to mind, make it drop in NF desolation area
also adding to the wish list:
please make Tormented and Eternal weapons dyable 
(like chaos axe)
skullcrest focus is hella cool
also there is some skins on npcs that can not drop - for example that one handed hammer thing on some weaponsmiths. also bmp or reward skins like deldrimor, imperial, envoy, ... or collector skins like norn/asuran axe/shield/etc, gemstone staff in moddable or os rng version would be dope. but I wouldn't want them to add too many else other skins would become incredibly much more unlikely to drop... I also like the armor idea!
I made an inevitably incomplete list of skins that could be added with some criteria: https://wiki.guildwars.com/wiki/User:Loggy/LimitedSkins
I love the ideas of adding NPC armors and costumes as available to players but the past 2 updates (PvE Elites and Profession Mods) have both been updates where minimal effort allowed for maximum gameplay change, so I think they will do something similar.
Now, since armors and costumes for NPCs are already exisiting assets it could definitely be easy to just add them to armor smiths as craftable armor and I'd love to see that.
The question that remains then is: What's the gameplay change? A third profession like some Stone Summit? Casters wearing medium and heavy armor when investing into those profession's attributes or wielding martial weapons? A way to swap certain skills in explorable areas? Making Summoning Stones permanent like Legios to cater to a decreasing player base and cheaper/more sustainable pcon use?
