Excellent idea. They have something vaguely similar at GW's figure museum in Nottingham, where there is a multi-level "skirmish" diorama involving a house with several floors and levels of cellars, caves etc.
It's a great idea for creating a figure display in a limited space. I like how you've done yours and I'm sure we'll see more similar displays on the LAF
I wonder if anyone might be able to do a WWI version with a trench system full of Germans and a Royal Engineer tunneling party digging a mine underneath?
I'd love to see something like that!