What are the limitations of current HDTV output implementations?
Custom Resolution driver Support is still very YMMV, its OK when it works, PITA when it doesn't. Its not intuative, its inconsistent across different inputs. The terminolgy is different between the manufacturers, there's not enough configuration for advanced users, and documentation is very poor.
Video codec support is also just OK when your use is supported , but poor if its not. Proper video handling is constantly suffering from assorted issues, and HD formats are the worst. Proper hardware acceleration of popular formats is only partially supported, and emerging formats as well as legacy formats take forever to be supported despite programmable processors. Software takes considerable effort on a users part, and lacks advanced configurations for advanced users.
It just shouldn't take a monster rig and an advanced degree to playback, output and encode video.