By popular I mean that material based on the universe is always being made in some form or another. Like after the OT, lots of books were being made about the characters. Lots of these stories didn't even involve the OT main cast, but random characters in the background or even new characters entirely that became very popular. Just look at Wookiepedia, so many long articles. I would spend hours on that site, like as if it was TV tropes or Wikipedia itself. So, without star wars is there any franchise that could take it's place in having an expanded universe that keeps interests in the stories, and has such an extensive universe like the old republic era?
Something important about the star wars franchise, is that it's expanded universe doesn't have to focus on the main movie characters to be popular. Just look at swtor, Kotor, the legacy era,etc.
Some possibilities: Halo, Harry Potter( a name change would be in order though)