I'm not too sure how I'd feel about this. One.. It's not REALLY Brandon's choice. He doesn't own the Wheel of Time world. He's not writing the book of his own accord, he was hired to complete the series by the person who is now (I'm assuming) in charge of the Wheel of Time franchise. Unless Harriet decides she wants more Wheel of Time stories, or releases the information for Brandon to write what he wants in the world, I don't think there's anything he could do, even if he wanted to.
Granted, I don't know how any of this stuff actually works.. this is all just what I'm assuming.
Even if he was given permission, I still don't know how I'd feel about it.. Finishing the last of the series as an homage to Robert Jordan, so that his fans can see the work that he was trying to finish for them despite being terminally ill.. That's on thing. Deciding to take that world, and expand on it even more.. I don't know if I'd be comfortable with that. I wanted to read more about it as much as anyone. Wanted to read more on the histories, more of the battles that are mentioned and flashed back to. And was definitely interested in some of the spin-offs Jordan mentioned. But without Jordan actually writing them.. It wouldn't be the same.