Just as a proof of concept, I played with making a developer using tannic acid itself. I analyze for tannic acid in water at work, and tannic acid is rather similiar to pyrogallol and pyrocatechol all rolled up into a giant molecule but less toxic than either of those two compounds.
I used the Pyrocat HD formula as a starting point - I found that it took a large amount of tannic acid to replace the pyrocatechol in the Pyrocat, on the order of several grams/liter (if I remember correctly) to get it to have a similar contrast index. It had a good stain as well.
I didn't pursue it very far, I just wanted to show it worked.