Heard the Casa amp/cab yesterday at Long & McQuade and was mightily impressed. The description "tight low end" may be loosely thrown around sometimes but in this case it's right on the money. I like the look of the class D head in a tube amp size head case but from a practical point of view it does seem a little bogus. If they'd use that extra space for a drawer for all the small things you might want handy (flashlight, AC tester, picks, fuses, sharpie, clip-on tuner etc.) I'd totally buy into the concept.
Is it a class D head or a class AB solid state? I was under the impression that it was the latter, but I could certainly be wrong.
As for the large, empty space below the amp in the headcase, I think it's silly but I totally get the look. You could put the amp in a smaller headcase (and perhaps a rack, though it's not clear from the photos on the Markbass site whether this would work without modification). Assuming no cooling issues, the headcase appears big enough to accommodate a second Casa head should one wish to mount two together.
As for a drawer, that could be a pretty neat DIY project if you wanted one -- might be that a rack drawer would work, but you'd have to check dimensions and mounting requirements.
EDIT: I was thinking class AB based on the size, weight, appearance, and more old-school vibe of the amp (at least as presented in adverts and videos -- I, like most at this point, haven't played one). 6.4 kg / 14.1 pounds (from the Markbass site), if that includes the headcase, is a bit on the light side for what I'd expect from a 500 Watt, transformer-based, class AB amp... I dunno, though, depends on the weight of the headcase. Maybe it is class D. Maybe class AB with an SMPS (that would cut some weight vs. a transformer). Class H (a la the GK stuff)? Don't know.