Zaps were always buyable with Dominion coins since the store first opened.
I confirm.
Initially they were hoping that some people would buy so many zaps that they would spend money on gokoins on dominion coins on zaps. They wanted a "consumable" and came up with zaps as that consumable.
This plan had two huge flaws. First was that you didn't get to play Dominion in the adventures; you were just paying to beat the level. They sucked compared to just playing random games vs. the bots, and the fix was going to have to be, making the zaps just a thing for people who were stuck. Second they never had a system where you could possibly spend money; dominion coins are too plentiful. If zaps had cost fantastic sums of dominion coins, whatever, no-one was going to pay for them for the joy of spending them to slaughter an adventure level.
I argued these points and pushed for content to be what was sold, and they seem to have come around. I expect they will try to sell campaigns at some point. I have no problem with that; it could totally be worth the price to buy one.