The thing they need to steer clear of is making the replay system or engine not based on actual Mount&Blade versions. If any of you played Shadowbane, you will know exactly what I am talking about. Once a new patch or upgrade came out for the game, any recordings that you made in a previous version were not usable once you ugraded to the new patch.
Shadowbanes recorder files were in its own format and was not a video format. Therefore you could not export it or view it without loading the actual game and opening it up in the recorder. Once loaded there was still no options to export. The only way was to FRAPS the actual recording.
If they cannot make it to export the movies in a video format, they would at least have to make sure the recorder will load previous version files (for any version after the release of the recorder) so that you can still FRAPS the recordings at least.
Personally, I would like to see an individual program that isn't attached to the main game. A new "record" feature is added to the game, either by just a button or something more intuitive. Then it records the battle based on your settings into a file format to your computer. Then you load the Mount&Blade Recorder player which will load any of those files and play them back for you. They could then probably develop video export options within that new program.
Good idea though either way.