Mind you my experience with RP servers is minimal - I play on a standard PvE server with little RP. But the few times I've dipped my toes into that pool, so to speak; I've found people kind of doing their own things with the lore and RP'ing as stuff like dual classes, impossible race/class combos, "special cases," and so on. They're obviously not pretending to be in an entirely different IP like Star Trek, but they're doing their own things with WoW lore and the story surrounding it.