There is some context based advertising in place already, via amazon (used to be thru some "invite only" ad service) but the volume of advertising is very low, only one ad per several visits, and I'd venture that the rate of adblock usage and non-clicking of ads is much higher among the DDG set. I hope they find a way to monetize!

Paid search results? Would it really be incongruent with what DDG is doing?

Ads. They are already running ads including amazon affiliate.

Acqusition.

They got investment. Who needs profit these days?!

If you're running a company in an industry that's being encroached on by Google, throwing some money at a serious competitor like DDG might be a good investment.