We can't add textures or texts above the ingame graphics. Addons can only change existing textures at some points or chnage the menus + behaviour etc. that got nothing to do with the graphics ingame.
As we can only get information about players we interact with, or at least we have the crosshair above them, or we are grouped with, there might be no way to add information about players "that stand in your line of sight" :-(
There are some addons that cna change the crosshair/reticle, show information about guilds, friends etc., change the color of the names shown at the reticle if you know the players.
-RainbowReticle
-Combat Reticle
-Info reticle
Just search for reticle
Or:
-TargetLookup
-ThurisazGuildInfo