Unfortunately you cannot swap 8950 motherboard to a non-Dell case.  The proprietary dell oem motherboard uses non standard form factor.  It is not rectangular.  It is not ATX or any known industry standard.  It would not fit any standard case without losing front IO ports. the only way to beautify the 8950 if you think it is ugly now is to mod the Dell case.  For example, mod the side panel to have clear see through window.  Add RGB fans or led strip.  You can also paint the chassis if you like. Many 8950 users have not yet found the case utterly horrible looking or abominable.  With some work or tolerance you might still find some redeeming value of the case.
Hey,Has anyone changed the Dell XPS 8950 case for another model? I think this case is horrible. I want to change it for a more modern one, but I didn't want to lose the front USB ports. And I haven't found any replacement cabinets.  
XPS 8950, case change?