You don't think the extreme radioactive rim lightning will harm some enjoyment in the game? There is already a health bar for your enemies when you aim at them, if they glow too then they can't hide nor flank you, the same goes to you for them
The rim lighting fades as people get closer to you, with ranges varying from map to map. But by the time you are close enough where you are "flanking", chances are that you wont be glowing anymore. Besides of which, if i see or hear someone, i check to see what team they are on anyway; either by looking at them closely or checking the minimap. It might take away from the game, it might add to it. Until i play the game, i cant say for sure.
But until I play it I will assume that SD is doing their best to keep the game enjoyable. The beta testers have a better idea of the drawbacks than people watching a handful of gameplay videos and guessing from there. Giving the player more information is seldom game breaking.