Assuming "Long wait of 10 years" is a reference to wc3 (which was actually 2002 but meh) and Arthas in terms of story, I'm guessing that hard mode will reveal a little bit more lorelol the same way Ulduar hard mode did. (There are some datamined files that support this theory)

Other than that, yeah, there aren't many more characters left from the WC3/TFT era with untold stories. Cataclysm for example is about Deathwing and Aszhara, both of which were only hinted at in both games. I guess the franchise is finally moving out of an (in-game) era.