Not trying to argue with you you here, but how did you come to understand that Darth Plagueis died in the AOTC timeline? I thought it was an "old Sith legend."
I guess this is Legends so, it certainly may not be true. But my source is this nerd.
https://www.youtube.com/watch?v=yQSr52qP1j8
IF his timeline is correct, Palpatine didn't kill Plageius until "the night before he was elected Supreme Chancellor" which by my account/understanding was in Attack of the Clones when Darth Jar Jar nominated him. I could see the argument for when Padme requested that Palpatine be granted "emergency powers" in The Phantom Menace. So, by this account Darth Maul would have been alive as Palpatine's apprentice while Palpatine was still Plageius's apprentice.
I guess it's all how it is taken. When Palpatine was telling Anakin about the Legend of Plageius the wise it certainly seems to be inferred that Palpatine was the "apprentice who killed him in his sleep"- although it's not explicitly shown in the movie for some reason. I would think that would be a pretty important plot point that I would have liked to have seen as opposed to Anakin rolling around in the grass with Padme and a space hippopotamus.
And since we're talking about Star Wars Anthologies, I wouldn't mind seeing one about Sidious and Plageius and how they planned to take over the universe and the under workings of that. Of course that's prequel stuff so there's a good chance that probably won't happen. They could also delve into Anakin's alleged virgin birth and settle things like this that the fans have formed theories about. Maybe call it Rise of the Sith or something like that and have Jedi Master Sypho Dyas and then Jedi Count Dooku sent to investigate a possible new Sith only to have Dooku turn to the Dark Side and kill Jedi Master Sypho Dias and use him as the alias to build the Clone Army. And then end it with Palpatine killing Plageius.