I think we're only going to see this aspect of DTV improve over the next few years. Encoders will continue to get better (and hopefully stations will continue to keep current), and stations will continue to get more creative in their offerings on the subchannels.
Quite honestly, the downturn in the economy probably could not have come at a better time for broadcasters, as I've heard from a number of people that have dropped cable and satellite once they discovered 24 kids programming with DTV. In the Twin Cities, we have 2 subchannels with kids programs around the clock (PBSKids and qubo). If people can see enough value in it now, plus the future potential for more free programming, they might jump ship and save the $40 or $50 per month.
I'd be interested to see if over time broadcasters might start to fight the educational programming requirements using subchannels as a way to offer more of it on a targetted subchannel that fulfills the requirement for the station overall.