Well, InWin almost did it with the H-Frame! Apart from the feet (which could be easily replaced or removed), it's exactly that: no plastic at all.
That's why I find this case so fascinating.
This is a 1 out of 1000 case, and then they marry it with a weird open air concept and "ruin" it by that.
Obviously there are no customers for all aluminum cases, or else other manufacturers would offer such products. No market for $1000+ cases.
High quality all aluminum cases are standard in High End HiFi, they are non existant in the PC world.
Like this Jeff Rowland power amplifier for example. Never ever seen similar "quality" in the PC world. You could say it's not necessary, but that's also true for HiFi, yet there they still exist, albeit the price point is in a different dimension.
Something like this for an ATX PC would be my "do it yourself" project, I'm willing to spend a few thousand $ for it.