The shuttle is actually an interesting idea...if it had a decent mobo. Both the amd and intel versions are subpar due to their cons...and due to the fact it's low end SIS chipsets. They need to put in a good 690G or G33 chipset in there. For a nas, 10/100/1000 is required for decent performance and I'd like to avoid using an add-in card for that. An add in raid 5 controller is definitely a possibility though. I think given the right parts, this could be a great suggestion though.
The Morex looks a lot like the Qpack/Microfly type cases, which is interesting. I've been kinda iffy on those as they don't really seem quite designed for the purpose....but it's certainly possible it could work.
The last choice looks like it's in NSK3300/3480 territory(although these would be no good for hd's), which are cute cases, but a quite a bit larger than the nas devices.
It's certainly a challenge as the idea is to make something that meets or beats all those $400-600 empty nas boxes made by infrant/thecus using off the shelf parts and a linux based server without sacrificing size.