First off - Thank you so much for providing a great tool.
Now, many say that GS is becoming more of a burdain than anything else but I have to agree. Unless someone else can come up with some other system to rate people to know if they will contribute in a pug or whatever, I say, why not use wow-heroes?
OK, so for this addon talk.
I know you must have a calculation method worked out, maybe it's set in stone, maybe you're redesigning it - whatever...
Did you ever think about maybe working with other addon builders like Mirrikat45 from curse to help you guys out and get an addon delivered?
Some people say that you guys pull more info from armory than just the current equipped items, but most info is now available from in-game character inspection (If you include achievements)
An addon that would get even close to your GS calculations would help a lot for us raid assistants etc.
I think you would see much more traffic on your site if you made an addon that actively compared the scores of each player and gave a representation of that data for users to make the comparison ingame the use of the website is limited as you would have to alt tab out and then enter a players info in to the website to get the desired information. Also the website is a great tool for bettering your toon and much of that could be worked in to an addon.
I think the biggest problem you face at this point is that a large portion of the populous is using gearscore due to its ease of use however and i have not researched this but i believe that GS dose not take in to account enchants or gems that an individual has added to the item where as it appears that WOW Hero's dose. I believe that if you put out an addon you would see at the very least the people that use the website all the time using the addon right off the bat.