As previously stated I selected the Blackmagic eGPU because it is what Apple promotes on their website. Because Apple does so a lot of people are going to choose it over other options.
Having said that I did ask you which Sonnet eGPU solution you have. I didn't see you provide a specific model number so I am going to chose what popped up first on Google:
http://www.sonnettech.com/product/egfx-breakaway-box.html
This solution measures 7.25" wide x 13.38" deep consuming a total of ~97 sq/in. Combine that with the Mini's ~59 sq/in and you have a total desk space consumption of ~156 sq/in. And this is without any "wasted" space. The Z440 consumes a total of ~116 sq/in. Thus the Z440 consumes ~ 40 sq/in less than these two components. If this is not the solution you have please provide the exact model so I can evaluate it. Regardless it shows that the Blackmagic eGPU solution isn't the only solution which "fits my argument".
You're not using a monitor, mouse, or keyboard with your Mini? If you are then why are you specifically calling attention to them with the Z440
Perhaps you should do so (not sure why you'd include keyboard / mouse / trackpad when they're used by both systems and thus would be a wash), you might be surprised. Your target is ~116 sq/in of diskspace (for now I'll ignore all the extra cabling and power requirements your solutions require).
Yes, I can easily plug in all kinds of things to the USB ports on the system. If I need a portable hard drive I can plug it into a USB port (or a Thunderbolt port if I should want to add that to the Z440). I have the option of using external things if external is a requirement.
I could do the same...if I wanted. Nothing stopping me from doing so.
I am not trying to change your mind. What you have works for you. What I am saying is that Apple's focus on only external expansion doesn't appear to save much, if any, deskspace over a small to medium sized tower. Thus I would like them to offer such a form factor for my use case (which I do not consider rare). The argument that external expansion is better doesn't hold water for a lot of use cases. Thus for people like me I would like them to offer an alternative. But they don't. The Mini with an ePGU is the only modern Mac solution which doesn't force people with my use case to buy a screen. For people with my use case it's an inelegant solution which doesn't appear to save mcuh, if any, deskspace and has a bunch of drawbacks. So when I read people say "You don't need PCIe slots because Macs have TB3 ports" I have to take issue with it for a few of the reasons I've mentioned.
