Hi,
found your post on google, looking for similar gaming mini itx projects.
I have a similar project in mind, to build the smallest gaming mini itx possible. I'm not planning going commercial with it, just building one for myself. Right now the case is in SketchUp drawing phase.
The case you are building was one of the two variants i had in mind, at least when it comes to exterior dimensions. But it's not the smallest possible.

The other variant, the one i plan to build, is the one you can see in the pictures bellow. I have not finished the Sketchup drawing of the casing, it's only a mock-up and i've not decided on how all the case panels will mount together...
The total case dimensions should be: 6.8"(H) x 4.7"(W) x 12.5"(D); standard 2 slots video card cooler and 60mm total height for cpu cooler. Direct air path, positive pressure only. Perfect cooling, no dust, but also no noise reduction.
-no optical drive, as i don't need one anymore (everything i have is on usb sticks or external hdds)
-the video card is connected with a 16x pci express flexible extension card; i bought one like
this and replaced the cable with an ~8 inch longer one. Tested and it works fine, no performance or stability issues.
-only room for 2x 2.5" drives (maybe 3, i don't know exactly), but it's fine for me, as i plan to use an SSD for the OS and programs: one 128 GB SSD and one 1 TB 2.5" hdd.
-the video card can be as long as 11", with any standard 2 slot default cooling. But i plan to use a Scythe Setsugen 2 cooler, the only 2 slot custom gpu cooler that i know of. Direct air path.
-for the CPU i plan to use a Scythe Big Shuriken 2 cooler, with its slim fan. Maximum cooler height should be no more than 60mm. But the decision on this is not final, maybe i'll add ~0.5" to the case height, to accommodate a normal 120mmx25mm fan. Direct air path, the air will be pushed by positive pressure alone, to the sides of the case (haven't decided yet where the exhaust slots should be, maybe only to the back).
-SFX PSU (400w-450W by Fortron or Silverstone).
-custom shorter cables everywhere, including for the PSU. I don't think you can hide the default PSU cables without increasing the length of the case by an inch or so. I plan to replace the fan also, so it's not a problem for me, but could be for a commercial case.
This is the absolute smallest possible mini itx system that accepts a full length powerful video card, by total volume. I've tried several other positions of these components, but this is the most compact one with little to no space wasted. The case could stand vertical, with no legs, or orizontal, but with legs, so the video card can get some air from below.