Well, tbh they never really gotten to much into the lore of the world.
Even in the setting book for genesys, Realms of Terrinoth, is just scratching the surface.
If you look at GW, they make these big campaign books with LOTS of story. They also make novels to expand the lore even more. Just look at what they did for age of sigmar. That was a completely new universe and look at how many books they released in such a short period. That is what FFG should do with terrinoth! The Realms of terrinoth has 30ish pages of lore... 30!!!!!! That is NOTHING. How am I supposed to play a rpg in this setting? I barely know anything.
Hire some writers, give them some basic lines of how you want the overall story to go and let those writers go nuts. Give them a creative space to work with. Just some guidelines and story rules and voila. A universe is being build.
What they can do to make Terrinoth unique and exciting? Nothing, they just need good stories. Warcraft 3 was a very cartoony game but it was the stories that got people invested. The Treachery that people felt when arthas went all lich kingy. How muradin, the funny dwarf, got killed by arthas. Etc. Novels are just words on paper which are very boring to look at but still people LOVE reading specific books!
Reading in 5 lines that some dude went traitory and tried to steel some magic item which exploded ... Sorry but who gets excited by that?!? Give us an emotional connection! Tell us how they gotten to be friends? Did one almost sacrifice himself to safe the other one? Or Did the evil dude become evil because he was trying to safe his friend at some point? Tell us about their training time. I can go on and on.
I love the cartoony style of Terrinoth and the miniatures. It's a very colorful style like warcraft which i love to look at. Warhammer is usually very dark schemes and so are most other fantasy games. The aesthetics of rune wars is fine as is.
A good example is Critical Role. So many people gotten invested in that because of the story. Critical role is basically just a bunch of people playing a rpg. So much fanart was created for it, which is incredible! They even made a rpg setting book for that world and it sold like hotcakes because everyone wants to make a connection with those characters from critical role and be a part of their story.