I wish they would just sell the case in mITX size. Then I could add more own OS and other hardware.
There are cases like this available. I looked at them a few month ago (approx. $180 for 5 bays), but finally settled on a node304 (6 internal bays) for my home server. I got the case for $50 (on sale on newegg), added the ASROCK H97 ITX with WLAN ($50 on sale), Celeron G3258 ($44) and CX430 powersupply ($10 after sale and rebate). The memory I used from my desktop (had 32 GB, so removed 16GB and added into the server) and I had as well 4 x 3TB WD Green in my desktop, which I added to the server (plus an old 120GB SSD as boot drive). I added as well a 8TB Seagate external ($200 on sale) and a 5TB Seagate external (paid $120 a while back) via USB3 for backups of the system. Got Windows 2012 R2 DataCenter from Microsoft (free educational license). Running right now on the box Home NAS, MediaConverter, Linux VM (OwnCloud), MSSQL VM, Windows Access Server VM and Windows Remote App/Desktop VM. I have approx. 7 GB Memory free on the box, which leaves plenty for additional VM's. The only disappointing aspect of this HomeNas/Server build is MS Storage Spaces or more specifically it's implementation of RAID5. I get with mirrored drives plenty of throughput, but writing to a RAID5 volume is running between 25 and 30 MB/s after the cache is used up. So when I transfer large volumes of data (some Datasets I use for analysis are in excess of 1TB), take forever to transfer to the volume. Overall the box cost me approx. $250 (excluding harddrives) and I take this anytime over any of the NAS boxes. I tried some of the NAS boxes (QNAP, Synology) and was very disappointed. If you have a bit of time (took me approx. 1 hour to build and approx. 6 hours to install and configure Windows 2012 R2) this would certainly be a better choice.
Getting back to cases look at the following:
Silverstone DS380 (8 hot-swap plus 4 x 2.5 internal) for $160
I believe Startech USA had a case that looked like the Asus or QNAP 4 bay units for approx. $180.