The radar idea has been implemented in Shadowbane.
I have mixed feelings about the idea. It can help cut down on hacking and griefing, but it also reduces role play and emersion . Hacker programs will give players \"radar\" and present it in a easy to see format. If the client program already has this feature, then there is little need to make a program to do such a thing. I am thinking about Everquest here. On the Red server using the hacker program \"show EQ\" you had a disadvantage to players that used the program. What this means in a PvP game is that you know how many, from what dirrection, and how healthy your enemy is. The element of surprise and terrain advantage features are gone. Griefers like to use game quirks and lag to attack players that are sure kills. If you can see them comming in time you can run away, teleport, recall, summon friends, hide, or what ever you think best. Invisiblility can be made to defeat radar, but that encourages hacker to make programs that show invisible players.
MMORPG gamers can be subdivided into two groups ( I am sure other subgroups can be made), players who ignore moral standards while in game and those who despite being in a vertural world still live by some moral code. Some MMORPGs favor those players who are ruthless while online. I am actually thinking of the old UO and EQ\'s red servers and not SB.