I am against this rule, as I think the direct question rule suffices for this point. For example, "Direct question, where in the blue fuck does it say that in your source?" This rule only creates more of a burden on the one providing the source while giving more incentive for people to not do a lick of reading or independent research. As someone who doesn't have a shit ton of time to do research, but still does research for a living, a rule like this would disincentivize me from posting things related to law or science because I don't have 30 minutes or an hour to run, find the source, place it here, and put the relevant portions in nice and neat little quote boxes.
ETA: I also think the rule could be ripe for abuse due to burdens of proof. We had a long debate with Paragon recently about how it works, but I am not entirely sure that various people on here understand the concept. For example, if I say that there are no black crows, the burden is not on me to prove that, but on somebody to prove that opposite so as to disprove my assertion. Nonetheless, I still made the initial assertion and a rule like this could require me to proof the assertion. On a page like this, where debates are common and burdens of proof might be hard to assign, a rule like this could place the burden on the wrong party and require a specific citation which cannot be done, resulting in a rule violation.