HD in MPEG-4 is on the way

The transition is a-coming. We're talking about the move from MPEG-2 to MPEG-4 compression for digital broadcasting. What we don't know is how everyone intends to do this. As an example, we've asked Dish Network how their HDTV receivers will handle this, since current models are only capable of decoding MPEG-2.
So far, we don't have details, just a nice response indicating that
"historically, Dish has always provided an upgrade option." True, but that doesn't give us a warm fuzzy feeling.

We are watching out for info and stumbled on to some of the technology particulars
through the UK, however. The reason for the transition is mainly bandwidth, which we knew. MPEG-2 uses 18 to 20 megabits per second
(Mbps) of bandwidth for HD programming, while the more efficient MPEG-4 will only use six to twelve Mbps.

The challenge here is widespread. How will each individual provider adopt to the new standard? What happens to all of the old equipement? Will today's digital tuners cease to function?
Oh, this is gonna be fun!