Good idea, in the context of low power CPUs and Thin Mini-ITX with built-in DC/DC converters.
Some thoughts about your implementation:
1) Why not just provide a standard (or thin) I/O plate cutout? Then no customization is needed for particular boards.
2) The top vent for the CPU looks restrictive. Bad for cooling, which is also bad for noise -- it will force the fan (if there is one) to speed up & make more noise. Make it more open. With a Thin MITX version, the CPU position is always the same -- again no need for customization.
3) Don't know if it's worthwhile to ship as flat pack kits, assuming it's simple enough to assemble. No glue, right? Perhaps it's small enough that the size difference will not matter for shipping. But it might.
1) Standard I/O plate cutout is good because it supports all thin ITX motherboards, but increases case width by at least 1/2" and makes case more fragile at rear side. However it's only 2mm plexiglass on each side. On my market Gigabyte thinITX boards are only available, and almost all of them (both LGA1155 and LGA1150) have very same I/O layout which this case can accommodate.
2) This case supports CPU-s like i3, i5 and even i7 (which requires more cooling capacity). I havent tried i7 on board, but i5 3570k got much better cooling with Zalman CNPS2X (currently installed in the case) than intel's box cooler, despite it's size. Top vent is designed as cold air intake only, which is why more openings are not present. Othre reason is that more top openings will ruin case simplicity and minimalistic design. Side vents are for hot air exaust. This mechanism forces air blown by cpu cooler to pass through all components like PCH, SSD and DDR before leaving case at side openings. Zalman cooler is almost silent at idle (30C/86F) and very quiet at max load for i5 CPU, not to mention pentiums or celerons. As you already said, this case is good idea only in the context of low power CPUs. Who needs expensive i5/i7 CPU without matching external graphics card which this case and motherboard does not support?
3) Net dimensions for disassembled case is 18.5x18.5x1cm (7.3x7.3x0.4 inch). Glue is not needed. It constist of 6 plexiglass pieces (top, bottom and 4 sides), 8 metal spacers and 8 allen screws.
I'm not familiar with sending packages abroad. Sure there is the way but i must make some calls to find out.
In meantime i made another miniITX case which is few cm higher in order to accommodate intel box cooler, with abbility to be mounted on VESA compliant monitors. It saves space on computer desk and 20-30euros for custom zalman cooler (depends on country), where cooling performance difference is negligible for use on low power CPUs.
Pics and additional info will be posted very soon.