MetroPCS this morning announced plans to roll out devices that will support free, over-the-air broadcasts from outlets including NBC, Fox and Univision. There’s no denying that users are increasingly eager to watch video on their mobile gadgets, but by trying to replicate a traditional TV experience wirelessly MetroPCS is making the same mistake Qualcomm and others have made: Users want mobile-friendly, on-demand video content rather than streaming episodes of, say, “Modern Family” or local newscasts. Adding DVR functionality — which won’t be available at launch — would be a big step toward making such an offering more attractive, but I’m not convinced even that would be enough to find much of an audience.