Have you ever found yourself waiting(or spamming trade) for 2 hours to get an RBG team complete?
Have you ever had to go with the wrong setup, just because it was too hard to find the right people?
Armory provides info on rating / last activity / item level, a website like guildox.com, have more or less updated info
Another site, theunderminejournal, have no problem with generating realm specific files for download.
Combine all this, and you get an addon showing you who on the realm has a preset list of conditions you set before downloading the realm specfic file.
Want a sorted list of all classes / roles with 1750-1900 RBG rating on your realm, with item level between 475 and 485, who's been actively playing wow the last month? Set the conditions, and download the generated list and put it into your addon folder. The addon will show them on a neat list sortable by role / class / rating / ilvl. Filtering out or in certain classes / roles / online / offline would also be a nice feature.
I know it's many stages to an addon like this, but it should be possible for the right group of motivated people to realize this.
I know there is an addon out atm, called oQueue, that will put your premade out there for others to join even if they are on other realms, but the difference to this addon is that you will have a list of people who is currently online, that may be interested in joining your RBG pug/team for the evening.
I could have sworn I already saw almost this exact request somewhere and replied to it, but I can't find it, so...
Doing this would require not only writing the addon to display the data in-game, but also setting up the infrastructure to support the out-of-game portion -- someone would need to run an Armory scan, generate an addon-usable data file, and push an addon update to Curse and/or WoWI for users to download on a daily or at least weekly basis. That's a huge amount of work, and a big time commitment. You could cut down on both the work and time by setting up a web server to do the scanning, formatting, and pushing for you, but that requires even more skills, and costs money.
Also, the only ways to find out if someone is currently online is to (a) add them to your friends list, or (b) perform a /who query on them, or (c) be in the same guild with them. This means that it it is not really possible to keep track of the online status of hundreds of characters without (a) constantly cycling players on and off your friends list and/or (b) constantly running /who queries, neither of which is really desirable.