We had the discussion with Divinity also and Lar said they tried it but it just wouldn't balance correctly. One of the things is that it's a game where killing gains you XP AND solving quests gains you XP. The problem with avoiding fights and giving XP for that is in my opinion that you can avoid the fight => gain XP, solve the quest => gain XP. Then come back and kill the lot anyway => gain XP. This needs to be balanced properly for all playing styles.
One could say thet sneaking nets you 75% of the total XP. But what if you kill the monsters aagin? Should that give you only 25%? What if your sneaking fails, what should the XP reward per kill then be? Every monster in the neighborhood would need to get 'tagged' after a successfull kill in order for this to work And how long should the 'tag' stay?
As there are no classes anymore, the option to tie the XP and percentages you gain based on what typer of character you play are gone too.
