Well Tainted Remedy does something a bit different than Sanguine Bond. Whereas Sanguine Bond is an instant win combo with Exquisite Blood, Tainted Remedy instead gives you the ability to build a deck that lets you play cards that would ordinarily gain life to instead cause your opponent damage. Early on, it wasn't hard to see Tainted Remedy as a sideboard card to thwart decks that gain tons of life, especially in Modern and Legacy. It also has a great synergy with Beacon of Immortality.
As predicted, Tainted Remedy did see some sideboard play, as seen in some U/R Prowess lists in Standard. Tainted Remedy even popped up in Modern a bit, too, as seen in this Abzan Midrange deck. But it wasn’t adopted to the degree that many thought it would be. Still, there’s been enough casual and Commander interest to keep this card on a steady rise over the past two years.
Honestly, all it takes is some life-gain deck to dominate the meta in Modern for people to turn to a card like this. Really, the best place for Tainted Remedy is in Modern or as a tech card in EDH. Still, cards like this can still be valuable in the long run. It’s not getting cheaper, although a reprint could tank its value.
Tainted Remedy isn't a card you'd see being reprinted to death, either, as Sanguine Bond has. What it does is pretty unique and it can hose a lot of decks. It’s one of those stash-away sort of cards, as it can't hurt to pick up least 2 or 3 copies in case it becomes competitively relevant all of a sudden.
While Tainted Remedy likely doesn't have a price ceiling of $15+ like Exquisite Blood, it’s not impossible for this to be worth at least a few dollars in the next few years. If there’s a great combo piece to go along with Beacon of Immortality printed in the future, this card could go out of control. In any case, Tainted Remedy is a great card to have in your Magic binder.