Swords to Plowshares is a one-mana white instant that lets you exile a creature, and then its controller gains life equal to that creature's power
Even without Magecraft, the 2/2 for two mana is playable
If you run Emerald/Steel and manage to get your discard engine running quickly, you could sap your opponent of any means to get ahead in the early game
Any such choices will be made separately when the copy resolves
Its unlikely the card will see play in Standard or Pioneer, but the demand will be enough for Commander players to keep the price at a decent rate
Funnily enough, I had a quick look at the Cloudpost deck that made the Top 8 of the very first Modern Pro Tour in Philadelphia back in 2011, and the deck contained four cards that are now banned Cloudpost, Eye of Ugin, Green Suns Zenith and Punishing Fire