Is the reaction check needed for marking your characters location? Admittedly, just not having the reaction check, unless they are actively aware of you, if that's possible, would be useful by itself. Even if you were still an available target for voodoo or later flanking attempts or whatever they decide to do.
After this stuff, all we need is a better version of the aye-phone, the ability to cut the lights, greater morale hits when they don't know what just killed their allies, and we would be able to do full on Predator or Sam Fisher shenanigans.