My personal position is we should indeed take basic questions on any aspect of AI, so I'm not suggesting we end our experiment accepting implementation questions, but, where these questions haven't attracted an answer on AI, should we migrate to SE:Data Science or SE:Cross Validated?
If a question is on topic, then it should stay here. Migrating is for high-quality, but off topic questions. This is why migrating a question involves closing as "off-topic". In this case, they're not off topic - they just haven't gotten an answer.
Now, why don't they have an answer? Probably because there's nobody on the site who knows how to answer it... or the right person just hasn't seen it. If nobody on the site knows how to answer a question, then the best thing to do would be to attract users who do know how to answer the questions, namely, "experts".
How do these "experts" find the site, though? Usually through content already on the site - it'll come up in a Google search or something. So to attract the experts, you need content, and if you send all the content away, then AI.SE won't get new users and the site will stagnate.
There's nothing wrong with having some unanswered questions around, as long as not all questions are unanswered. And if that happens, the site's got a big problem.
See also Meta.SE guidance on migrations.
Questions older than 60 days cannot be migrated, even by moderators. I don't think we can expect questions to always be answered in two months — from my experience on Super User, it's not at all unusual for months to pass before the right expert stumbles upon the question and solves it. We therefore have a bit of a catch-22 here. Even if we could ship out old unanswered questions, that's probably less than ideal for site growth; see Mithrandir's answer for more on that.