Durability.
I travel a lot (most of my long term friends live miles away from me) and the 3D printing jobs we've got here in brazil are... "awful", to say the least. That adds up to the fact that hardware in here tends to be expensive as hell.
With that in mind, i prefer the strenght of steel, instead the low cost of acrylic or 3D printing composites.
The smaller you go, the easier it is to make it durable. I produced one that used wood panels, and used an external brick. That one felt very durable but I understand.
If you're based in Brazil it would be hard to design and manufacture one since you can't handle logistics when most of your market is outside your country.
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For your personal use, I think it would be simplest to modify a case or use one with a brick. I modified MX500 case to include an internal psu and use a pico type psu. It worked very well.
And aside from that, I'm still shopping around for price quotes to see if it is feasible or not. I'll get in contact with slinger as well.
Assuming you get the case designed to where you want it, are you looking to get it produced? Or are you just frustrated that the market has not made something for you?