Crossbows in reality are too slow to reload. This fact just can't be magically over looked even in TES. It also doesn't fit because Skyrim is low tech. Magic is a very rare occurrence in Skyrim. Even a crossbow would be a little high tech for Skyrim. I wouldn't be disappointed if Crossbows were added to the game but I definitely won't be disappointed if they aren't in because there are many factors why they wouldn't and not very many why they should be in. The only factor that would warrant them being in is diversity in ranged weapons, that's it.
Spears must be balanced not cuted out, in morrowind spears have long reach and and fast attack pushing back enemies to frequently, but oblivion also has frequently staggering in melee combat, does removing of spears from oblivion fix it, no it doesn't.
But thats was fixed by mods like
Doc Block Recoil Stagger
http://tesnexus.com/downloads/file.php?id=35933
Duke Patricks - Everyone Or Just Vampires Now Bob And Weave
http://tesnexus.com/downloads/file.php?id=15103
IMHO how to balance spears
Spears fear of shields and two handed swords, its historical documented, Zweih?nder even created for destroy pike and spears, thats not just some big sword, its instrument of taking tactical advantages in combat.
So we can block attack with shield or strike with zweih?nder and damage spear when enemy try parry, spears can be dodged by nimble enemies
Spears moderately fast (slower then short swords) have long reach and awesome pierce strike but slashing attack is not potent like blade has, they are lighter then two handed swords and hammers but have similar reach, they can be cost less then swords, and much less durable.
Spear was one weapons thats early humanity create, spear symbolic savage hunters how about Hircine without his hunter spear?
Spears was one of mass produced weapons in medieval since creating an spear was much less time-consuming exercise then an sword, they have awesome tactical characteristic like armor piercing and long reach, Pikeman was outdated only when firearm become powerful enough to replace spears.
About crossbows ok, Skyrim is too low tech for them, but how about other marksman weapons, how about throwing weapons?
Again in Oblivion developers leave only bows they say it was hard to make all other marksman weapon, but did they see this mod for oblivion?
http://tesnexus.com/downloads/file.php?id=7822
http://www.youtube.com/watch?v=QzOsBAPoWQE
Thats mod add throwing stars in 6 November 2006 via scripts
Todays Unnecessary Violence and Deadly Reflex make it even better, is thats hard to make more then only bows with total access to engine?
Dark Brotherhood Assassins and Dunmer Morag Tong assassins and other nimble characters can use darts, throwing stars and throwing dagger and knifes, nords, orsimer ant other strong characters can use throwing hammers and axes even throwing spears and javelins, Giants can thrown stones.