YouTuber xLetalis has been on the hunt for a particular easter egg in The Witcher 3 after quest designer Philipp Weber dropped some hints about it. Weber had previously tweeted at xLetalis in response to a video he'd made about the character Vivienne, who is part of the Blood and Wine DLC, saying, "I wonder when they will find Vivienne's last secret". Fans got hold of the idea of this "last secret" and asked Weber about it during a charity livestream earlier this month, during which he said "it's on Skellige" and that it "goes quite a bit further" than they might expect.
After some hunting, xLetalis has found the mysterious easter egg. To explain what it is, I'll need to get into heavy spoiler territory for a particular quest in Blood and Wine called The Warble of a Smitten Knight, so you've been warned.
During this sidequest, Geralt investigates a curse affecting a lady-in-waiting named Vivienne de Tabris. The curse has progressively been making her look more and more like a bird, specifically an oriole, and she's resorted to magical ointments to disguise the beak, talons, and feathers spreading across her skin. There are a couple of ways to cure the curse, one of which involves transferring it to an oriole egg, though this could result in Vivienne's death seven years down the line.
If you go through with it, the curse will be lifted and Vivienne will decide to use whatever time she has left to travel the world. First she'll go to Novigrad, and from there to Skellige. (Although she doesn't always follow through on that final step since she's supposed to move into a room at Kaer Trolde's inn that Yennefer may be staying in, depending where you're at in the main quest.)
With help from The Witcher 3 console commands, xLetalis moved Vivienne to Skellige then sped up time so that seven full years would pass in-game, and found that Vivienne does indeed drop dead as Geralt warned her. It's a little underwhelming that thanks to an issue with the cloth physics, in xLetalis's playthrough she fell with her dress at a right angle to her legs, and that she can still repeat her greeting dialogue from the floor, but it's neat that there's any kind of follow-up on such a rare circumstance.
Not to rain on the parade, but though xLetalis deserves credit for being the first English-speaking easter egg hunter to discover this, German-language site GameStar published a story mentioning it back in 2020. Elena Schultz interviewed a couple of members of CD Projekt Red about secrets and easter eggs, then went hunting based on the hints they dropped and found the same thing: if you wait for seven in-game years, you learn Vivienne really dies a natural death. At least that's how my high-school German translates, "Vivienne stirbt das wirklich eines natürlichen Todes!"