I had a similar idea before:
However I have some questions about the idea:
How the saga will be played?
Will it be a choice that comes in Episode 4? Will it be a separate purchasable DLC? Or it will be an entire separate game?
Now for the next question:
What are the saga features?
It’s not a good idea to just speak about the sage, there should be more details about it, and better, stuff that make it preferable other than the other Episodes. Is there a new enemy? Weapon? Final Boss?
There should be something that makes the saga unique, the story alone isn’t enough.