i haven't tried but i really doubt it would work. magma hasn't advertised at all gpu's can go in there, neither has sonnet with the expansion chassis. I don't think the gpu will recognize at all without it being in a 16x slot, plus the sheer fact that the power supply of the magma wouldn't even be able to sustained a beefy video card. it's a nice idea, and maybe one day a chassis will come out that harness 2 tb ports for 16x worth of lines so u can toss a gpu in there, but as of now I'm positive it won't work. but even without that, just being able to have a sas card, i/o card, and than a third card like rocket or usb 3, 10g ethernet, or whatever else offers a lot of freedom. a single unit to really simplify things, and keeps someone like myself who's invested heavily in my tower setup from buying all this redundant stuff just for the sake of giving a laptop more options. i can just take the cards i already have out of my tower or any extra components i have laying around and toss it in the sucker.
as for tbolt cable managment. i think really the worst part is that the apple tbolt cables are incredibly long, which is nice, but it just makes it a spaghetti mess, and the material of the rubber isn't the easiest to wrap up. I'm looking forward to custom length cables some day.