Good god please no. Talk about yanking all the skill from a game. More and more games nowadays are implementing invisibility (killzone crysis, ghost recon, halo ect) and in every one of those games it's gimmicky and cheesy. The only time you will see anyone use it is when they're looking to snag a free kill by camping in some dark corner. It's a horrible concept that does nothing but promote camping - a large step backwards for any developer.