When a card is reprinted as a regular rare in Standard, one expects the price on that card to drop. We certainly saw this when Thoughtseize and the Onslaught fetchlands were reprinted, though when the painlands were reprinted in Magic 2015 we saw Battlefield Forge go as high as $9 due to the increase in demand.

Goblin Piledriver has observed a price spike since the announcement of its reprinting, which could likely be primarily attributed to people looking to flip them quickly before the supply increases and the price drops. Alternatively, it could be that the card is expected to be very good in both Standard and Modern, causing it to demand a high price tag. It's also possible that buyers were expecting Origins to be a relatively unpopular set, opening up the possibility for a regular rare to command a high price tag.

I personally don't buy the Modern hype, and do believe in Origins as a set. The Modern Goblins deck just doesn't offer anything that looks better than Affinity in the same vein of decks or even anything that looks favorable against a deck with Lightning Bolts. Meanwhile, Origins has all kinds of interesting cards and a cycle of exciting Planeswalkers, leaving plenty of reasons for many to open packs. As such, I would imagine that we'll see Goblin Piledriver lose significant value in the coming weeks, even with significant Standard play.