I'd go so far as to say that there will definitely not be anything new in the WoT universe aside from River of Souls and the encyclopedia. Everything I've read has shown that both Brandon and Harriet seem uncomfortable with the idea. There are literally two sentences of material on what the outriggers were to be about. I can't imagine that there's much more for the prequels, which don't even seem to be what you were interested in.
And it seems that there is pretty much universal opposition to any Star Wars-esque series of authors writing in RJ's world. While unfortunate for what is, from what I've read so far, an incredible saga, I think it's for the best. For many years, Jordan wasn't even sure he wanted someone to finish the main sequence if he passed away. I don't think it's justifiable to keep writing in his world. I'm also super excited to get more Stormlight, so if that's your thing, perhaps that would be a suitable replacement for WoT in the years to come.