Maybe of interest to people looking for the same type of solution:http://www.satasite.com/4-drive-2-5-inch-sata-backplane.htm
This apparently allows installation of 4 2.5inch SATA2 drives into
a single 5.25inch bay.
The price is good, the storage/size ratio sounds awesome, but it
seems that these allow only SATA2 and not SATA3 transfer speeds.
Although they have active cooling, the fact that drives are close
together may mean that this solution is more prone to overheating
than others. Note that I do not own one of these, so cannot speak