The stage I'm finding myself with excess bark at is after starting treeplanting. I'm growing trees for wood color and for silk, so maybe past the "sprucecap" stage but still "early game"? I definitely have leather but I'm getting more bark than I'm using for leather, on account of growing trees for silk and construction.
I like the bark armor idea, but it wouldn't really satisfy my desire to have something to do with this bark at this point since I could just make leather armor. I like the idea though, it would be nice to have cheaper armor to try out armor mechanics on.