-try to make signs, torches etc. placeable on the blocks
-preserve sign text, ContainerBlock contents
-Permissions. Yes, you "convinced" me that you really want and need it. So you shall get it.
-add configuration support, so the admin can choose which blocks can actually be used as secret doors (e.g. bookshelves)
-possibly add LWC-support
-clean up the code and release it