There are a load of unused npc's in the base Morrowind game and the DLC's also add another handfull.
So after a little inspection of them, I made up a nice couple of categories:
THE VAMPIRE REJECTS: These are a lot of npc's possesing the script of one of the three vampire clans, not only did they never really get a class or level set up, most of them don't really fit in with the existing clans anymore.
Aundae Vampire Script: Aleri Duro, Ano Dran, Estalenya, Nush, Pustula Baenius, Silasson
Berne Vampire Script: Chulz, Dinere Hlen, Morn gra-Khatub, Peregrina Cnisia, Velis Thirothan, Gerrilgor
Quarra Vampire Script: Garalo Andalas, Ninimilk Addinibi, Rangela, Varnis Stieve, Waylas
Out of all of them, only Estalenya, Peregrina Cnisia and Rangela are the ones that fit in their respective clans, considering the rest, maybe someone will find a purpose for them (I have an idea, but I don't think it would ever get approved)
ALD'RUHN UNDERGROUND PEOPLE: This case intrigues me, supposedly there were some shady dealings in Ald'ruhn which never made the final cut. The people associated with this al carried a small key, in the final game, Lirielle Stoine and Ilmiril still carried this key around, Ilmiril is also mentioned in Sottilde's Code Book. Three cut npc's also posses the key; Dalos Golathyn and Fomesa Tharys, two Wet Ears in the Thieves Guild and Llandreri Selothan, an agent. I really hope someone reworks it in Skywind <3
LEFTOVERS: These people can't really be placed in any of the groups above;
-Ulwaen, an Imperial Legion spearman, nothing more.
-Ather Belden, he has the same level and rank as the Ald'ruhn Underground thieves, yet doesn't have the small key so I couldn't place him with them, he does carry some torches for whatever random reason.
-Cinia Urtius, the master trainer Medium Armor, probably already thought of, moving on :p
-Corrudus Secunia, He's an early version of Cunius Pelelius, the script Cunius has also is named "corrudusscript" , maybe make Corrudus take over Cunius' role and degrade Cunius to a manservant.
TRIBUNAL: I couldn't find anything noteworthy on any of these npc's; Dirver Relas, Dro'farahn, Edre Retene, Hulgarth, Myn Farr, So I'm just thinking of repurposing them.
BLOODMOON: No big description needed here;
-Cingor, he's an early version of M'nashi.
-Grandfather Frost, he's easily the most recognisable character on this list and an early version of Uncle Sweetshare.
-Valgus Statlilius, a male Imperial Legion Trooper at Fort Frostmoth.
-Kili the Long, because of her high level and name I suspect she's a Skaal.
-Hallvaror and Wind-In-His-Hair, both are male, level 20 shipmasters, maybe they were earlier versions of Basks-In-The-Sun, maybe they could all be part of one crew in Skywind.
Non-existent People: these people are only mentioned in the game and do not exist in npc form, this list could grow later on;
-Huleen in Maar Gan, she apparently is a member of the Mages Guild and a friend of Edwinna Elbert, considering her name, maybe she's Argonian.
-Tulz in the Dren Plantation, an argonian slave mentioned in the Note To Hlevala.
-Tarvus Beleth, the actor you replace in Tribunal, apparently he has vanished from the globe.
-Sados Relothan, he is the owner of a house in Raven Rock, nothing else is known.
If you made it this far through my giant text, I want to say thank you for your time and if you have any ideas or would otherwise like to contribute, don't hold it in.