An immediate problem I see with this is the only way to search for a specific player would be to hard search the herald XML files.
What I mean by this is say your on Pendragon.. you'd have to search all the guild xml files till you found the player you are looking for. Lets say you were looking for JoeBlow on the Pendragon server and he is in guild number 281 (XML files are labeled by guild number). The program would have to do a search through XML files
http://www.camelotherald.com/guilds/Pendragon/1.xml to 281.xml
This would put quite a noticeable amount of requests on XML files from your IP and could lead to mythic easily figuring out what your doing.
Now I think the map plugin can show the guild of players. I can't remember to be honest but if it can, and that guild name can be converted to the guild number somehow then you could easily find the info on someone loaded on the map screen because you'd only have to scan the one XML file. So it wouldn't be nearly as noticeable as the previous.
At one point Mythic had a search feature to search for a player. I would figure out a way to use that to make it look like your actually searching for the player but I can't find that page anymore, anyone know where it has gotten to?