I feel like one of the appeals to using DuckDuckGo is that it simply isn't Google and, therefore, doesn't come along with all the ethical baggage. That's true now, but who's to say that will continue to be true in the future? At the end of the day, the same forces still drive large businesses to cut corners, costs, and creeds if they want to compete effectively with one another.
There are no guarantees, but if they're not currently amassing data trails then they won't be an attractive acquisition target for a data aggregator. If they ever change their privacy policy, you just stop using it.
