Whilst sites like Wowhead & the Armoury collect character data, they keep everything on their servers, and I'd like to have a record of my character's deeds on my on PC. As such, I'd like an addon that can query WoW for character information and then save it, ideally in a per-character (though I daresay there'll need to be some per-account data too) format that's easily usable outside of WoW (eg if I want to convert the output into a CSV file, it shouldn't take me hours to do so).
Given the amount of data WoW stores on each character, it's probably best if the addon doesn't automatically scan everything when you log in, but only does so when, say, you tell it to scan your mounts. In addition, it should know to skip stuff it's scanned as completed / acquired before, so as to reduce the amount of requests it's sending to the server.
Keeping the addon updated shouldn't be too hard. There will need to be a list of maximum valid IDs for items, achievements and so on, and a list of reputation IDs to ignore (a list of valid reputation IDs might be shorter, now that I think about it...), but beyond that there should be minimal work outside major changes to addon code in general.
Topics to scan*
-Items in bags/bank/void storage
-Character Stats panel (# of HKs, deaths in AV, etc)
-Quests (completed: yes/no)
-Achievements (completed: yes/no & date)
-Reputation (just do the factions visible in the reputation window, skip hidden ones etc)
-Pets (ID, level, quality)
-Saved transmog outfits
-Character bio (time /played, hairstyle & colour)
-Garrison/Order Hall/War Campaign followers (IDs, quality, upgrades)
* A background task should automatically note when any of these topics (except items) are updated. Telling the addon to scan achievements again because you just got one is silly. The item exception is because you don't want this addon recording a vast laundry list of junk items, but knowing that you've still got your Holy Mightstone will be nice.