Well there's an idea, instead of having to redo the brick system for blocks, leave the current system as static blocks and make a seperate class of objects that support basic physics and a range of motions. JVS has doors down, but they don't have any physics to them. Rotating/moving platforms that carry and fling crates and barrels and people and vehicles could be fun, even if you could use only 10 in a server or something. Dynamic bricks that you could build small things out of (I understand you can't put a skyscraper on wheels) would be neat too.
With events that started and stopped them, animated bricks like gears and propellers and shafts and things would look pretty cool even if they didn't actually work. Imagine having a button that started a windmill, which turned a set of gears, which turned a shaft which ran a grindstone. Or an island and boat held up by propellers. Even if it was all fake, just animations playing, it would look very cool, and it can already be done.