I just remembered that I saved the oak cubes from a mulberry mead I made a while back. It sat on oak for about 4 months on medium toast French Oak. I am wondering if I reused that oak in a sour if it would have any affect at all.
it likely won't add much oak flavor, but it may add some complexity from any carrying mead character. plus, brett can metabolize some of the sugars (cellubiose) in the wood, so it'll add a different note from that as well