So far I don't really see that answers to off topic questions are an issue for this site yet. Most other SE sites (probably around 99%) do not have or needed to discourage users from answering off-topic questions, I don't see why we need it either.
We are also in a better shape than cstheory because most off-topic questions are actually migrate-able if this even becomes an issue, while the same cannot be said about cstheory before cs.SE. Additionally, our set of off-topic questions are considerably smaller compared to cstheory, so it is inherently harder to ask an off-topic question here compared to cstheory. Our site resembles more like 99% of the other SE sites that don't adopt this policy, and cstheory is an exception among all of the SE sites, we are nothing like cstheory except we share some of the same topics.
Maybe if in the future, that this is indeed a real problem, we can talk about it again, but for now, my vote would be a solid no.