What can you do with known plans and recipes?
I tried to sell them at a few vendors, but none will accept.
Each weights 0.25. After a while I amassed quite a weight through them, and it'd be a shame to just drop them! I don't know any other players to gift to.
Duplicate plans do not appear to have any uses currently and whether or not a use for them is planned is unknown.
Besides gifting them to other players, the best thing to do with them is to simply drop them due to them taking up inventory space. I always check to see if I know the recipe/plan first, and if I do, I drop it.