This is a very intriguing idea... probably only so, to me because I'm about to head into my first build.
I see the obstacle being that participants are going to be mostly limited to people building their first cab, or pros building for other people, which creates a huge disparity in skill level.
Unfortunately, unlike the biker build off shows, the cost of the cabinet isn't likely to be covered by the producing television show. And we amateurs can't afford to eat the cost as part of an advertising budget.
I know that a lot of this would be like car shows, where part of the score would be the elegance of the wiring etc... things that nobody but builders are going to appreciate; although these elements would be missing, you might get some participants for a virtual cab build. Even that would turn into a contest of skill at 3d rendering though.
I'm intrigued and just throwing out ideas and obstacles that might have to be considered to make this a success.