It's going to need to sustain that growth for a decade to be of any reasonable size. Google gets approximately the same number of search queries per day as DDG has in its entire lifetime (~11 years).

Edit: The problem in sustaining this growth isn't just marketing either. With increased traffic come increased server, maintenance, and engineering costs which may not be possible to support with untargeted ads as advertisers won't pay big money to show ads that have poor conversions.

I'm curious how untargetted they are - if I'm searching for python, how untargetted is a python book ad? I'd be more inclined to purchase that rather than a remarketing adroll targetted ad that's just spewing me the same item that I purchased 30 minutes ago

Sounds interesting. Got a link for that? And I’m saying that as a DDG user.