So, what should be the policy on "do my homework for me" type questions? Will this forum reject all math-content questions, to concentrate on math-teaching and math-learning questions?
Questions about mathematics are already handled by the Mathematics and MathOverflow Stack Exchange sites. I believe that "do my homework for me" questions do not belong to this proposed mathematics education site.
I don't think this SE should cover the material being learned, but rather the process of learning itself. In that light, I don't think homework questions should be on-topic - rather, (precise, well-posed) questions about the value of homework in teaching might be, or whether homework should be individual or group based in a proof-based undergraduate class.
Math.SE will remain the best place to ask such questions on the SE network.
There are mathematics education courses (and programs and degrees...), so it is conceivable that this site could get on-topic questions which are homework questions in that field.
My guess though is that the phenomenon that exists on math.SE -- namely "This question is not identified as a homework question, but a qualified observer would believe that it is overwhelmingly likely that the OP is asking it in the context of homework [not necessarily graded or done for a course; a better term might be "exercise"], and treating the question as deserving an answer rather than an explanation, hint or teaching request is probably ruining its value to the OP" -- may not be as prevalent for math education questions. In other words, something could be someone's homework question but also be a "real question", i.e., something of interest to practitioners in the field.
But it seems reasonable to reject questions that have only math content and no math education content: there are already two other popular sites for math content questions. Right? Presumably questions with both math content and math education content should be on-topic at either site. Which site would be preferable sounds like an issue that is best addressed organically once/if the site actually exists...