Appleinsider posts a description alongside artist renditions of upcoming changes to Leopard's DVD Player (5.0) software.
Improvements range from fullscreen chapter navigation with chapter thumbnails, a time bar for visual scrubbing, satin platinum highlights, equilizer and other preferences.
No word on any additional HD-DVD or Blu Ray support have been noted.
Update: The most recent Leopard DVD Player apparently does include the following references to both HD-DVD and BluRay in the settings file:
"sd dvd folder" = "VIDEO_TS";
"hd dvd folder" = "HVDVD_TS";
"blu ray folder" = "BDMV";