We're a large casual raiding guild. We have people who raid hard and people who don't at all. As we progress deeper into the content, we've found that it helps us (the officers) to keep track of who is ready for which raid. We're currently using a spreadsheet that has rows for each toon and columns that say Kara, Gruul, Mag, ZA, SSC, TK, etc.
The system has supported this for a long time. Look at the "Keys and Attunements" section.
However, custom fields are indeed coming, and are currently in development (there's a massive update in the works, for which I haven't released many details yet).
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It's all in the reflexes.