Placing a trapdoor on the back of the seat and then putting an item frame on either side of the trapdoor, you can create a folding theatre seat that is stackable to both sides, and you can even decorate by placing items in the item frames, as I have with orchids.
FYI: The trapdoors DO NOT actually destroy the item frames if placed correctly, so this design is extremely effective for decor in maps or even if you want to make a literal theatre!
-ElfyPers0n