A very interesting point, and one I agree with. Ferdinand and Isabella did not sponsor Columbus's expedition as an exercise in exploration for its own sake...but to bypass hostile powers more efficiently trade with China and India. If there was no economic reason for the voyages of discovery, how long would it be before the New World would inevitably be discovered?
My guess is much later, when Denmark returns to reassert sovereignty over Greenland and Vinland. OTL, it was already too late for them to make any headway in the American mainland, but if they were the first to rediscover it since their Nordic ancestors, we could see a larger Danish realm around Newfoundland and Quebec.