The main benefit I see of making it Maul is so he can have a little bit more to do in the only film that he is in, and to not add confusion to there being three Sith in the film if you were to also have Dooku thrown in there.
You could just have Maul do more of Sidious’ dirty work to help keep Sidious more mysterious in TPM.
It also might be easier to do that than Dooku, because you could have hologram Maul hooded, so you wouldn’t need to make Maul’s mouth move appropriately with the dialogue a lot, or maybe not at all.
Plus, you have a lot of possible dialogue to pull from The Clone Wars and possibly Battlefront 2, so maybe if you trimmed up those scenes you would have enough to make their conversations work.
While you could also pull lines for Dooku from the Clone Wars, since it is a different VA for most of the show, the voice could be noticeably different.
Though in the end such a change might not be worth the effort.
To change the subject, I had another idea for Revenge of the Sith.
I have seen this idea brought up before in videos and on here as well I believe, but the gist of it is that a part of the reason why the Jedi are less trustful of Anakin and why he isn’t given the rank of Master is because he killed a defenseless Dooku, and that you could slightly rewrite a few scenes to establish Anakin’s action having this consequence. And then, when Mace tries to do the same thing Anakin did, but with Palpatine, it gives Anakin all the more reason as to why he would feel betrayed by the Jedi and their hypocrisy. He gets punished for killing Dooku by Mace, but now Mace can do the same thing?
The bad thing is that it is never established that any of the Jedi even know Anakin executed Dooku, and there’s really no way to change the dialogue to establish that.
But I had an idea today. What if you had Mace, Yoda, and maybe Obi-Wan watch a hologram recording of Anakin killing Dooku on the bridge of the ship (which they could have recovered from the crash). You could use elements from the scene in Attack of the Clones when Obi-Wan contacts Mace and Yoda about Jango Fett and the Clone army, where his hologram is being projected from a little pedestal in Yoda’s chamber. And you could use the wide shot of Anakin standing over Dooku’s body as it falls to the ground for the hologram.
You could intergrate the hologram pedestal into the deleted ROTS scene where Yoda, Mace and Obi discuss Palpatine’s growing power. Maybe at the beginning of that scene, they watch the recording, then get a few silent reaction shots from them, then they start discussing Palpatine. But since the hologram might be a little unrelated to their conversation, you could just add a very brief version of the AOTC scene with the new hologram, and then have a few silent reaction shots of Mace and Yoda to imply that this information affects their trust in Anakin that we see throughout the movie. And this scene could be placed early on in the film.
To make sure the scene isn’t too short, in the wide shot you could have the hologram show Anakin and Dooku dueling, then cut to shots of Yoda and Mace watching while we hear lightsabers clash in the background, then cut back to hologram when he kills Dooku, and cut back to Mace/Yoda for their reactions. You could even use the brief shot of Anakin grabbing Dooku’s wrists for the hologram, then cut back to either Mace or Yoda with maybe a surprised look if there is an appropriate one. And then you could freeze on the final shot of hologram as the Jedi masters absorb what they just saw.
Anyway, just another idea I had.