Sneak is pretty broken in skyrim so I thought I'll fix it. I don't have much experience in scripting but I believe things I want to fix are pretty simple things so the biggest issue I might face is finding out what settings I need to tweak to get the effect I want.

Overall plan:

Smarter AI
Piss poor AI is the number one problem in stealth gameplay. With high sneak skill pc is pretty much invisible (my charater has 100 sneak +20%sneak from perks and +25 from sneak boots, no muffle and he is silly op). To fix this I'll tweak the sneak formula which determinates how visible you are. Also AI doesn't simply forget that you are there if they see a dead friendly or they have seen you and you have vahished (ie enemies are alert longer and become alert easier.

• Easier to get detected
  
• Next to impossible to use heavy armor
  
• Enemies are more alert NOT THIS EVER AGAIN: http://www.youtube.com/watch?v=lHbF9ynGZV *
  
• Friendly npcs are more "aware" (I'm not sure how I'm going to achieve this) NOT LIKE THIS(first minute): http://www.youtube.com/watch?v=StC4xGmzS20
  
• Patrolling npcs (a script or leveled list gives them atleast one torch) use torches when light level goes below certain level (I don't know what determinates light levels) and they also light up static torches (2:15) : http://www.youtube.com/watch?v=DGIgXeGC6Dg

*enemies are not alerted if enemies die a "natural" death (traps, death by other hostiles, illusion with quiet casting, poisoning via pickpocket)
Using this mod changes gameplay a lot http://skyrim.nexusmods.com/mods/8070

Sneak tree changes
Current sneak tree has two paths. The the right damage part and the left "random" part. I think damage bonuses you get from items and perks are fine (yes even the "30x knife instakill creamed with cheese" -perk) but the left "random" path consists perks that are somewhat pointless (by either making you even more op without any actual gain, many of the effect can be also achieved via alchemy, magic and items).

• Revamping some perks and paths. I mainly want to change silent roll into dodge (kinda like in oblivion) which allows player to perform dodge while standing or sneaking. By double tapping movement key (wasd) the player can determinate which direction he wants to dodge.
  
• New path/perk which allow player to disguise as enemies (like in shivering isles). I'm not sure sure which factions can be disguised as. Propably guard factions, civil war factions, necromancers, forlorn.

Global changes
What happens if player is detect and is forced to deal enemies in a direct combat. Well there is no problem as light armor has really good defence and there is almost no diffirence between maxed light and heavy armor.

• light armor vs heavy armor. I wan't to make light armor a lot more squishy. Heavy weapons can easily stagger lightly armoured targets. This naturally creates an unbalanced situation where couple heavy armor enemies can easily kill the squishy thief. To balance this I want to make all melee attacks use stamina (knives use less, warhammers more) and give daggers assasins critical hit chances when enemies stamina is low (this will also apply to player if their stamina is low)

I propably will make my mod compatible with this: http://skyrim.nexusmods.com/mods/2700

Stuff that comes after this
Thieves arsenal in skyrim would be fun and useful (because oblivion didn't have many high places like in skyrim).

Thx for reading and any tips and ideas are welcome.

Not to dissuade you, but have you seen the http://skyrim.nexusmods.com/mods/10456 mod?

Thanks for that link.

I guess I'll start modding that mod instead creating everything from scratch or atleast use it as a reference.