I think the FIOS approach is to bring a bunch out all at once, rather than add a new channel here and add a channel there. It must be. Otherwise they would have added the channels that are available now. Maybe the .TV filler isn't live yet, who knows? But the nationally known real channels that are HD should go HD ASAP on FIOS. We all know Encore, MLB, Crime and Investigation, another others I cannot think of off the top of my head are live.
What about the Retroplex (They are calling it Starz Retro) and the other new one? They are two SD channels, and have been live for a long time according to the Starz/Encore website. They haven't turned those on either last I checked.
Verizon may feed things out nationally, via their Super Head End (SHE), but they still need to make changes regionally (at their VHOs) to accomodate any new channel feeds. For most of the channels, I'm not sure what the delay is - they started that roll out some time ago, and it just stalled. As a result, some markets have Encore HD, as well as Starz Retroplex and Indieplex (our market have both of those already too - they were turned on around the same time as Encore HD). The other markets will get them too... and I believe they were supposed to have them already - they must be hitting some technical issue that's stopping the roll-out.
I do know that the .tv channels are causing them problems. According to other sites, those aren't just straight linear TV feeds - they involve some IP connectivity - beyond that, I have no understanding of them. But apparently Verizon IS having problems turning those channels on at all.
Again, not sure what the hold-up is, but they started the new channel roll-out and it's been put on pause for a while. As for them just adding one or two channels at a time - they've done that before. You already used the MLB example. And they've done that before.
As for their bandwidth - they still have plenty. To understand how much just requires a little basic bath. Verizon currently runs all their channels via mpeg-2. They do no additional compression, which means that they can carry 2 HD feeds per QAM channel, or 8 - 9 SD channels per QAM channel. This latest expansion (what went on last summer), including their analog elimination, gave them 135 QAM channels. Let's say, for sake of argument, that Verizon gets to 150 HD channels per market - that uses 75 QAMs, leaving 60 for SD. And they can fit over 500 SD channels in that space. Since they don't have 500 SD channels, they can easily expand beyond 150 HD channels. Given how many SD channels they currently carry, I think they can get to close to 180 HD channels, using their current architecture.