consider this - when the DS9R was still ongoing, and The Soul Key still either before publication or just recently published, do you think it's plausible (not if it's possible), that TPTB had *no* plan / idea / direction as to where the DS9R story goes, as far as the Ascendants arc is concerned?
Furthermore, I find it's perfectly plausible that one of our esteemed authors had already submitted such an outline, or that TPTB have already sent out requests for such submissions.
Marco Palmieri presumably had a broad-strokes plan for what would happen with the Ascendants, but as I understand it, he let the authors themselves come up with most of the specifics and was open to having the plans evolve and change in repsonse to the new ideas the authors brought in. Marco was laid off eight months before The Soul Key came out, so his focus at the time would've been on getting that book edited along with The Never-Ending Sacrifice. Given the timing, it's possible that he might've solicited an author for the next book in the series, but not certain.
(And he wouldn't have sent out requests for submissions, but would've more likely handpicked an author and worked with them to develop the next novel.)