I'm reading the Darth Plagueis book right now. I'm only about half way done, but this really seems to be a lot of source material they could draw from for what we know of ep 9. Has anyone read this? The story of Darth Plagueis (the wise
) seems to be centered around his long term plans for control of the Republic (he is really playing the long game), as well as his fascination with the force and how to control it to extend life. He conducts a lot of experimentation on different species to see how the midi-chlorians co-exist with their bodies, and how that might be used to his advantage. It also shows him finding Palpatine and bringing him slowly into his plans (which so far from what I have read lead into what we see in ep 1), as well as Sidious finding Maul.
This book really seems to be setting up how some of these rumors for ep 9 could be played out. It also shows how Palpatine learned from his master and could really be playing the long game here too.
As a side note, after reading this book, I'm almost convinced that JJ had intended Snoke to be Plaguesis.