A lot of people in this thread don't seem to understand OP's initial complaint, or even understand what's going on, so allow me to explain.
Firstly, the old Ysera is not being removed from the game, or buffed into the new Ysera, it is being moved to the legacy set. The new Ysera card is a completely new card.
Dream now costs 1, and can only target enemy minions, Nightmare now gives +4/+4 instead of +5/+5, Ysera Awakens now costs 3, and only affects minions, Laughing Sister now costs 2, and Emerald Drake is unchanged.
3 of these 4 changes are very clearly nerfs, making the original Ysera much worse than before, which should be considered a nerf to Ysera.
It does not matter that this Ysera is rotating to Wild, it is still a nerf, and players who own Ysera should be able to disenchant it for full dust value.
People should read this first and then judge the problem. I think people think we're complaining about the new standard Ysera, and not the old one. Or think the nerf only affects the new one.