I dunno. How many people would be interested in a story line in the years between episodes 6 & 7 that followed the original characters? If they got the right writers/directors etc and the right marketing I'm sure Disney would be able to use such a thing to make a guaranteed return of investment.
I think you're right, that they should try move things away from the plot lines of the main nine episodes, but I'm just saying I don't think it's that set in stone.
Hobby writer, here's my sci-fi;
https://www.royalroad.com/fiction/36579/endeavour