According to what Brian Herbert wrote about the the story behind "Dune: House Atreides", Frank Herbert had left behind literally thousands of pages of notes, ideas, and sketches.
There are many Dune fans who state that Brian would have done us a greater favour by publishing his father's notes, than writing additional novels together with Kevin J. Anderson. Although Brain and Kevin deny this, there are many Dune fans that are not very happy with the novels that they have produced so far, and consider their working as cheap novels, not literary S.F. works like the books written by Frank Herbert. I am among these people, and I do not consider their additions as canonical.
I have to say I find the idea that Frank Herbert had already thought out this character GP Omnius and was going to introduce it in his last book, rather odd, especially, because it conflicts with the idea of the Golden Path. It is clearly that the Scattering was going to surpass all previous scatterings in order to avoid the destruction of mankind. It is suggested in "The God Emperor of Dune" that this destruction is caused by machines. But no where in the original series is there a suggestion that these machines were related to the "thinking machines" of Butlarian Jihad. The use of "seeking machines" might suggest a link to "hunter-seekers" developed by Ixians, as explained on Wikipedia: Golden Path. (I do have to say that I do have problems with Brain and Kevins intepretation of the Butlarian Jihad as being a physical war between man and machines, and not a religious war to ban out the use of powerful computers.) Please remember that both Paul and Leto II could see in the far future, and thus would have seen the copies that GP Omnius has send into the far reaches of space. I also do not see how it could fit in "The bitter medicine of a Sheeana future?" as Murbella sees it. Furthermore, the last book strongly suggests that Daniel and Marty are the Enemy, or at least others of their kind.
From this interview one can already conclude that they are not going try to follow the outline as closely as possible. During this Brain said:
To me Brain and Kevin will lose their credibility if they do include elements from their own books and do not decide to publish Frank Herberts outline in some form, preferable as an appendix of this "seventh book", such that we can verify that these elements were indeed original invented by Frank Herbert himself.