From a quick look at recent migrated-away question statistics, the vast majority of the questions we get which are migrated away from the site go to English Language & Usage (which, given that that and Writing Meta are the only two migration targets available to the community, isn't terribly surprising). Only a small minority of questions that do get migrated to English Language & Usage are rejected; a migration is rejected if the question is closed on the target site as anything other than a duplicate of an existing question.
There's a small handful of questions which are migrated away from Writing to other sites in the network other than English Language & Usage.
Very, very, very few questions are migrated from Writing to English Language Learners. In the past three months, we've migrated as many questions to The Workplace as to English Language Learners, and both of those migration paths require the involvement of a diamond moderator.
That said, while a community migration path is certainly nice as it cuts down on moderator workload, if a question genuinely should go to a site to which no community migration path exists, no matter which site that is:
- Put the question on hold as off topic (you can use "Other" for this, since we don't really have a specific "this really isn't about writing at all" close reason); a question that isn't off topic here is not a migration candidate even if it would also be on topic elsewhere
- The rationale for that last point is simply: If a question is on topic on more than one site in the network, it's up to the OP to choose where to post it; we shouldn't impose our choices on them, though we can suggest that a question might get better answers on some specific other site in the network and mention that the question can be migrated if OP so desires
- Once the question is on hold (or immediately if you're willing to live with the risk of the flag being declined or aging away if the question isn't considered by the community to be off topic here), raise a custom moderator flag on the question and suggest migration to whichever site you feel is a good fit for the question, or even better (especially if the user is relatively new to the network) suggest that OP raises such a flag
- Having the OP raise the flag increases the OP's awareness of what's happening to their question, which is a good thing
If we start getting a lot of migrations to English Language Learners, it might be reasonable to set up a community migration path for that, but:
- Right now, in my opinion we just don't have sufficient volume to justify taking up a slot for such a migration path
- For the specific case of EL&U and ELL, I can see a clear risk that it would be confusing to people, seeing that the two sites have at first glance rather similar subject scopes, with a fair bit of apparent overlap
So, before we set up such a migration path, the community should make the case that it is needed by showing that we actually would be using it at least semi-regularly. For the time being, that means first putting the question on hold as genuinely off topic here, then having a moderator migrate it away. The community already has all the tools for the former, and a custom flag is by far the easiest way to do the latter.
Also, for clarity's sake: I am not saying that we can't have a community migration path to English Language Learners. I just don't think that the data currently shows any indication that one is really needed. If we do start to migrate a reasonable number of questions to ELL, or if our migration reject rate to English Language & Usage starts to go up, then it may well make very good sense to set up a community migration path to cover that need.