It was all the way back in season one of The Vampire Diaries, of course. The show hasn't worried about doing too much in a long time. It's easier to name the tropes this show hasn't used.
Remember season one's promo images? (Photo: CW)
Speaking to EW, executive producer and showrunner Julie Plec said that the mother of Matt Donovan's Zach Roerig, Kelly (played by Melinda Clark), was originally going to be revealed as a succubus. It was part of the show trying to figure out how many supernatural beings were too many. They drew the line at the succubus.
There's even a cut scene of Kelly sucking the life out of someone out there. Plec said:
We shot a great scene with her sucking the life out of somebody and hooking up with Damon and everything and then we thought, "Oh my god, where in the hell are we going to go with this? And if this is season 1 and we're going down this road, then what other demons, etc. are we going to explore?" We got cold feet, rightfully so, and we pulled back on it and so we never actually followed through on the story.
Actually, that is plenty fair. You probably want to stick to fewer elements early on in a show -- especially one as soapy as this one, where there was a lot to get through. This would have been a bit too much, probably. Plus, it's always more fun to ramp it up over time so the audience can look back and go "Wait, how did we get here?" The Vampire Diaries is currently in its eighth and final season.