I think the height of the board (213mm) precludes most ITX cases*, especially smaller ones, so it would have to be a microATX case. Smallest I can think of is the IN WIN BK series, but with the limitation that I don't think any card that has the PCIe power connectors on the top will fit, as it's quite narrow. You'd need something like the R9 Nano, with the power connector on the front**.
*with certain exceptions *cough*
**some people call it the "back" but IMO those people are smoking crack
That is very very interesting! I wonder how high the top HDD part is -- it already shows a 3.5" disk which is 1" thick and a Flex ATX PSU is only 1.59". If that fits then I could use the originally intended space for an NH-U12dx-i4 and go with an EPC612D4I. Ho-humm
As for disks, I could just use a SATA-mSATA adapter, it's only 57*46 mm and squeeze it anywhere.
I believe V3+ | V-Series | Jonsbo | Cooltek this is the smallest at 10L. I am not 100% the motherboard fits but from pictures it definitely looks like.