Okay, if RJ had lived and completed the series in a satisfactory way what outrigger stories would you have wanted him to explore. Assuming he would have written the other two prequels to follow up on New Spring and at least the rumored planning of writing a series or one-shot novel around Mat and Tuon reclaiming Seanchan.
For me I think I'd had liked a series centered in the early years of the AB world. When Aes Sedai were powerful and plentiful and playing a more direct role in global geo-politics. Not sure I care too much about the specifics of the story told, but I'd love to get a much better understanding of the Compact Nations rise and fall. Perhaps this could even stretched into the Trolloc War years and give us a birds eye view into the first woman to become Black Ajah and how she managed to build the organization.
Alternatively I'd like to see the AoL explored, possibly from the POV of one of the Forsaken, perhaps one of the top level Forsaken who did not get trapped in the Seal, but had to cope with the early stages of the Breaking and evading capture by Latra Posae Decume and her forces. Maybe even give us some understanding of how the Prophesies came along and culminate in the White Tower being created by the various Ajah's.
Also of interest to me would be a little time spent with Shara and learn more about how they came about.
For me, it would have to be Fourth Age WoT making contact with a lost AoL colony. Be it from pre-war, or even a Shadow faction from the war.
With the AoL tech level, and they easy access to both alternate dimensions and other planets... It's only natural that they'd have SOME kind of off world colony/ies. Even the war and the Taint couldn't of killed off everything.
The Forsaken were even finding multiple stasis boxes full of Shadowspawn in the few years they were free. I doubt the Shadow was the only one who came up with the rather blatant idea of waiting out the war or Breaking in one of those.
Civilizations like the AoL aren't that easy to kill. They're like freaking cockroaches. Always crawling out of the woodwork as soon as you think you got the last of them.
But really... All those random unpredictable factors that play into how the Fourth Age would develop are what I like most about it. It's why they needed something like the Dragon's Peace. They'd of been completely screwed if they didn't have it to give them a bit of breathing room to adjust and realize just how much their world has really changed in a few short years.