It seems like a low value proposition if their most enticing feature is the ability to view Google results. Moreover, if Google added a "!d" command to show DuckDuckGo results, I can't imagine anyone would use it.

A negligible number of people are willing to sacrifice tangible functionality for intangible feelings of privacy that almost certainly will never impact them in any meaningful way. DuckDuckGo needs to make large improvements to their search results if they want to capture anyone outside of this niche market.