Also support/compatibility with Civil war overhaul should be ensured. He already makes use of some detection system.
Apollodown said there should be no compatibility issues with Civil War Overhaul.
Maybe also take a look at alternate start, since it makes you friendly with some factions at least at the start of the game.
There's a vampire patch for Alternate Start. Also, when you equip faction armor, you're temporarily removed from opposition vanilla factions. You're also temporarily removed from the Thalmor, Vigil, and Forsworn vanilla factions when you equip the respective disguises. However, that somehow doesn't work with Alternate Start's respective starts, so you still have to manually remove yourself from those factions if you started in them. Honestly, Alternate Start really shouldn't use factions that way it currently uses them.
It would be nice if your chance of disguise would be drastically reduced, if a dead body was found or a trap activated/sth stolen,... Anything that causes NPCs to be temporarily alerted.
I'll look into it.
It would be a nice addition, that when using one or more equipment pieces of a faction which is hostile to another one, the latter are more hostile towards you (blades armor and thalmor) but if you wear full equipment or remain in their sight too long, they get immediately hostile.
If you dress like a Thalmor agent, the Thalmor's allies and enemies will be yours. If you equip a Thalmor robe and a Blades helmet, you'll still be disguised as a Thalmor agent because the body armor is the minimum required for most disguises. I could penalize you for wearing the opposition's "colors" so to speak by eliminating the delay before rolling for detection and dynamically changing the suspicious NPC's expression to Disgusted. Actually, that brings to mind another good idea: when the NPC is watching you, I could temporarily change their expression to Puzzled. I'll try to get that implemented for the next update.
You'll need to have a look at the main quest where you infiltrate the thalmor embassy. If you could provide a stealth option for this quest, it'll need to be 100% working.
There shouldn't be any issues, although it could be harder if/when you equip the Thalmor Robes instead of the Elven Armor. There's nothing in the embassy disguise script that would suggest a real problem. The Thalmor might not turn hostile if you're wearing the Thalmor Robes; on the other hand, like I said, you don't have a 100% chance to remain undiscovered like vanilla, so using the Thalmor Robes would probably make that quest more difficult, even if you are Altmer.
However it might be useful, if you add an option to perform a stealth attack with all bonuses without needing to attack in sneak mode if you successfully got close to a tricked member of a faction.
Having just discovered that I can kill sleeping targets instantly in Requiem, I have no problem with adding an attack bonus when you're in disguise and behind an NPC, but I am wary of making disguises a go-to strategy for everyone who wants to cheese their way through the game. For example, if I had this bonus implemented, you could wear Daedric armor, summon a Dremora with the Atronach Forge, walk up behind him, and assassinate him for free, risk-free loot. Over and over and over. I try to prevent exploits like that.