Increasing multicasting like that begins to take its toll on the quality of the HD feed. Honestly, as far as I'm concerned, stations doing 1080i (CBS, NBC, CW) shouldn't do more than one subchannel aside from the primary, and those doing 720p (ABC, Fox, MyNet) shouldn't do more than two. Ideally those numbers would be zero and one, respectively, but I know that's not going to happen. Each station has only a finite number of bits, and the qualty starts to get really bad as you try to compress things more and more.
That said, MyNet does so little HD that I believe some stations may choose to make MyNet SD and do some other service with the rest of their bandwidth.
- Trip