I don't see any problem with the temps of the HDDs in our review. Anything less than 50C is perfectly fine, there's bazillions of HDDs which do fine for years of 24/7 at >50C. Besides, all of the higher temps were only seen when the CPU was under ridiculously high load -- which rarely happens in a home server.
Up to 50C may be perfectly fine, but I am never happy if mine go above 40C in late November, as the ambient temperature could easily go up by 5-10C in the depths of summer which will lead to a direct 5-10C drive temperature increase or an automatic noise increase if fans are setup to compensate. This is probably me just being a bit pickier than most people. FYI I could not see the ambient temperature of the test-room.
A simple fix for the fan/cooling issues is removal of the stock fan & shroud, and installation of the biggest quiet fan that can fit inside the case under the drive bays -- probably a 120mm. Then, all the exposed venting around the fan could be blocked off with aluminum tape (or some such thing). This would turn the case into a positive pressure box & likely improve cooling for everything.
No doubt it would although I am still unconvinced by the whole design, that and the best price I have found in the UK is £118 after taxes and DOES NOT include a PSU, this makes it expensive enough (in the UK) for most people to forgo the size and hot-swap and use any number of mATX cases also saving a little on the motherboard in the mean time.
I have a very simple solution for a cool, quiet 4x 3.5" drive bay + 2.5" bay ITX box that could use positive pressure and have no issues with cooling and could also be hot swap to boot, all I need is some easy to use 3D designs software where I can create "components" e.g. HDD's, PSU, motherboard etc to precise measurements and build the case around those components.