After seeing Froome's TDF ride, I could definitely see droppers making their way to road bikes.

On a side note a personal prediction of mine has been that suspension forks for road bikes will eventually appear as well. As manufacturers look for new ideas to force new road bike sales, I think they'll turn more and more to mtbs for inspiration. I could totally see smaller, lighter, less travel suspension forks appearing with the argument that they keep road bikes from jostling around as much on rough pavement, allowing for a faster, steadier ride.