I'm going to build your rainbow stepper tonight. It looks more compact than what I've been accomplishing. I like that you've used different length axles rather than more bricks on top, which is what I'd been doing.
Instructions for my adaptation of Akiyuki's GBC train car are now available at http://mocpages.com/moc.php/353031. This version required less than one intervention per hour at the most recent weekend exhibit.