Isn't masquerading sponsored follow-up question a loophole around the "guiding principle" of not wanting to influence the user here? I must say though, there's no easy way out for pplx since ads, by definition, compete for user's attention (and an unrelated / unobtrusive sponsor link / question / reference would be no good for the sponsor; which is to say, the sponsor is pplx's customer, not the end-user).