@shuffman37: I'd be really interested in knowing what your hosting provider for that would be, because that's a truckload of bandwidth and speed you'll be needing there. Unless you happen to have unlimited money supplies?
I don't think YouTube could consider subscriptions, really. The site isn't associated with that in the public's mind; that kind of business decision is one that should happen at inception. Later on it's a recipe for disaster.
I think the real reason behind this, however, is pressure from media conglomerates.