As ELL has matured over the past hundred or so days, I think we're now reaching a point where ELL is big enough, mature enough, and has enough dedicated high quality answerers that the biggest impediment to growth is the number of ELL-style questions on ELU being consistently answered on ELU rather than being migrated to ELL.
ELU has a lot of ELL-style questions posted every day, and so I am asking on meta before contacting ELU to ask them to begin a policy of migrating such questions to ELL rather than leaving them to be answered on ELU. I will also be posting on ELU meta to get community consensus over there to encourage posting suitable ELL-style questions to ELL.
But before I do, we need to agree on what questions we actually want from ELU. Unless there is a community consensus against me doing so (if you disagree with any of these points - add a meta question opposing it below), I will be asking ELU mods to migrate questions on ELU that fit the following critiera:
New - we don't need any old and dead questions being posted to ELL, and there's a high enough volume of new ELL-style questions on ELU, that we'll be busy enough dealing with those as they are migrated to ELL. ELU moderators should (in the first instance) migrate only new ELL-style questions to ELL.
Where the question is clearly about the typical 99% of English usage that is normally of interest to learners, and not about the atypical 1% of English usage that is of interest to fluent speakers of English studying English at degree-level or equivalent.
Where the question doesn't fall below the ELL criteria of being specific, not being a dictionary lookup, and not proof-reading, and doesn't focus on the history of English, writing advice or help with complex or old English (for which writers.SE and ELU might be more appropriate).
Where the question is clearly on-topic for ELL and off-topic or border-line off-topic for ELU (usually by virtue of being "general knowledge" on ELU).
And where the question has not already been asked and answered on ELU (in which case it should be marked as duplicate and linked to the ELU answer).
For questions that are in the gap between being possibly suitable for both, I expect ELU will want to retain such questions on ELU for the time-being, and that's fine.
I also expect this policy will change as ELL matures, so please keep your suggestions specific to what we ask ELU to do now, given where ELL is today, rather than a policy for some hypothetical future ELL. There will be plenty of opportunity to refine this policy as we go.