Boing Boing describes a $25K bounty for hacks to the new DirecTV PVR to allow usinng a different (higher-capacity) hard drive, multiple drives, etc. They state that they specificially don’t want anything that will bypass the DRM or Tivo’s service fees.
Those caveats are a shame, because the best upgrade to a Tivo would be to throw away the Tivo software and run MythTV on it instead. That would give the users more features (including support for larger disk drives), but it would also have no DRM and no service fees.
I’d encourage anyone who wants a DVR to set up a system with MythTV rather than buying a Tivo or ReplayTV.
Disclaimer: I was one of the engineers that created the original ReplayTV. But I don’t have any financial interest in any DVR company now.