I imagine this is why we don't have ESPNU HD.
I'm sure ESPN is wanting ESPNU on a more common tier, either Choice or Xtra. Having it on a premium pack gets many less subs, and thus less revenue to ESPN.
CBSCH moved recently, so we know there is hope. It will probably be contingent on when their current contract is up, or if not soon if ESPN offers more favorable terms to get it on a lower tier. Although DirecTV isn't launching much HD until D12 is up, there is still some room. I suspect if they had/could get a deal on ESPNU it would go up quickly, Directv being so focussed on sports.