So my understanding is that the reason Duty Recorder can't be made available for every duty is because of server strain. so i started thinking about how they could off-load the task to client side and i think i have a workable idea.

Incorporate the Recorder into the launcher for the game. the technical logic is that activating the function in-game would signal to the launcher to record all traffic received from the servers. since we can see other player's fighting animations that proves that we do receive the data regarding their actions, so the integrated recording software would receive that data too. If recording directly to the game is too hard on resources, then record to the launcher separately and maybe even save the replays uncompiled/unanalyzed. this would then be a separate process to be activated in the launcher itself outside of regular gameplay. By cross-checking the animation data we already receive from the server with the internal database of all the game's moves (which it needs to display them to you in the first place) the compiler/analyzer has all the data necessary to assemble the entire scene and all its happenings which can then be easily viewed.

worst case scenario is that we only receive the display data from the servers, meaning we essentially stream the visuals we see like we're watching a netflix movie while playing a given duty. though the file size of the game itself seems too big for that to be the case, and examples like google Stadia prove that such a method is bad for performance anyway.

Therefore, the client side software renders the environment we're fighting in, every character and their animations including the boss, and probably the battle effects too while the servers would be coordinating positional data, keeping health bars and damage values synced up, and other things like that. in this most likely case, enabling Duty Recorder across all duties to be handled entirely as visuals and processed entirely client-side should be easy to implement and would massively boost fan-made content creation as it would function as a video equivalent to g-pose.

Even in the worst case scenario, this would still be enough to be able to compile personal combat data like mapping out dps over the course of a boss fight. even in this case with its content creation capabilities ham-stringed, it would still be an invaluable tool for players and would enable the Duty Recorder to be expanded to include all duties.

If this isn't done officially by square enix and yoshi-p, then a third party mod maker can make it a thing themselves, and since doing so would not affect a player's interactions ingame, it would not be a ban-able offense according to ff14's current standards for mods.