I doubt that a movie player will be written for HH mode because mplayer was implemented into the current firmware because they could just port it over. Writing a new movie player from scratch would be a huge task.
The reason the battery life is pretty poor while watching movies is that the cpu is working at full speed when it doesnt need to. All processing is handled by the video processor so the main cpu speed can be lowered. Gph have said that this will be fixed in a future firmware
A HH movie player is possible, but unlikely, and for speed, it would still require the 2 processors, so would probably use up the same amount of battery power.
If its been said once its been said a million times. Linux isn't the problem. The problem with battery life is due to the second processor, the LCD, and the EXT port being "on" all the time. All can be fixed with a firmware upgrade if and when its released.