So, my idea is relatively simple; paper walls, like the doors and walls in kung-fu movies.
6 paper arranged in a pattern like iron bars makes 16 wall pieces, which work a lot like glass panes and iron bars. These are special; light is allowed in, making it as bright as the block on the other side of it, but do not allow mobs to have line of sight.
Now, if you take 6 of those walls and put them in a door pattern you get a door. Now, because of how MineCraft works, they can't slide, but you can at least have doors that match your walls.
Please, tell me what you think and any suggestions that could make this better!