This is a list of suggestions and ideas that may or may not be at some point:

• Chairs.
• Support for custom scripting/games to the Arcade.
• Putting a named book into a bookshelf with the same name will make it emit a Redstone signal.
• Redstone Gates.
• Entity filter on the detector.
• Addon mod to add Biomes O'plenty variants to blocks.
• Planters and pots.