It has space for four Pis in Adafruit cases and a netgear router all held together in one case.
I am planning o cluster mine, in which case (pun!) I am going to have to think about something similar, but I don't want to use up my precious lego!
I will probably end up using an old 19" rack that I have spare, and mounting each Pi on a piece of 6" x 4" perspex along with a cheap USB hub and a 9V Regulator so that I can power them both from a single 9V DC supply.
But that's a long way away after I have finished the modular synthesizer, the drone etc....