Animation is the least of its problems, the whole implementation is the problem.
If they put it in they should make it more than what it was in Morrowind, a dagger on a stick, the same weapon as everything else, except with longer reach.
One of the problems I can see is the reach. Realistically, a spear should be useful when there's a distance between the spearman and the enemy, if the enemy steps beyond the spears reach, you wouldn't be able to hit them. Now I don't know how can you implement this in a first person game, especially in a way that it won't make it annoying.
Well for first try think beyond of morrowind please, morrowind implementation of spears ten year old and was designed when engine wasn't flexible, if think only about flaws of previous implementation and don't see around any other examples of good implemented spears there is too much features will be removed, better to think in other way
How about implementation of better blocking and parry as well about dodge first?
Did you play with Duke Patricks combat mods before?
For example look this video
http://www.youtube.com/watch?v=Q-d6eS4159c
NPC have much better combat AI then vanilla Oblivion combatants have, did you see how he avoid strikes and use shield for block?
Enhanced overall combat AI can handle spears well by just dodging strikes or by block them with shield or counter spear with Zweih?nder, and can be usable not only for spears but for more interesting combat in overall,
besides there other games also thats have spears and they have them implemented well like in Mount & Blade or Demon's Souls.
I test awesome Duke Patricks mods with some spear mods and they work in awesome way, there is just one problem modders create all needful assets after four years after Oblivion release, lats years have many major breakthroughs in scripting and modeling, devs have all of this assets from beginning they not need make them from scratch, engine logic opened for them they have powerful tools for animations is thats hard implement features thats modders already done for Oblivion?
There is problem devs reduce features if found them flawed instead of spending some time and fixing them its similar to Alexandrian solution too bad such cheap solutions way to oblivion of series and turned at end into Procrustean solutions which torturing to many of us.