Here's a look at the PSU area with an HX1200i installed.
The total height of shroud is 125mm (4 15/16") and you've got about 34.2mm (1 11/32") between the PSU and the shroud. So you'll have plenty of space to potentially shove various controllers and devices in here.
Again ... thinking about what the more artistic types could do with this has me pretty excited. You could do some interesting stuff that show through the hashes on the top of the PSU shroud and you'd have plenty of room for something in here. The only challenge would be airflow - if it needed cooling of any kind.