Over the past few years, I have spent some time on ELU and ELL. (I deleted several accounts, so my current account is very new, in case you are wondering.)
I understand that ELL was formed because of the dropping standard of questions asked by mostly learners of the language. If I recall correctly, however, Robert Cartaino never saw the need for a separate ELL, and it was Jeff Atwood's intervention that made ELL come into existence just before he left SE. (Forgive me if this is wrong.) At that time, I agreed with Robert's view that there should not be two separate sites. I will list a number of observations I have made which you may not agree with:
In many cases, it is difficult and largely subjective where to draw the line between whether a question fits better on ELL or ELU. Many questions that can benefit one community of users also benefit the other, if one is seriously interested in the language.
Learners of the language actually learn grammar formally and ask many interesting and technical questions about grammar on ELL that many native speakers do not know about. On the other hand, many native speakers actually ask questions such as single word requests which should not be the focus of ELU anyway.
Many questions asked by learners are actually non-trivial but get interpreted as trivial by some native speakers. Hence they get downvoted and closevoted more than they actually deserve. Sometimes, a seemingly local question may be part of a larger, global theory of the language, and illuminating answers can salvage a less than perfectly phrased question.
On some days, the quality of questions and answers on ELL seems way higher than that on ELU. ELU, despite what is advertised, is not actually for linguists, etymologists, and serious enthusiasts, and never will be. The point is that standards on ELL are so high and ELU so low that the two sites really are the same.
It seems pretty arbitary which posts on ELU get migrated to ELL, and looking at some of these and how similar they are to other posts, we might as well migrate half of ELU to ELL. If the sites are merged, we will not waste time migrating questions between them, and the single merged site can benefit from shared human resources. It would be easier for genuine enthusiasts to see all questions at one glance, and users not interested in particular kinds of questions can just choose to ignore them.
Before you downvote this post, do spend at least a month on each of the two sites, and perhaps you will realise that you agree with me. I propose that ELU and ELL be merged, because they were never meant to be separate in the first place. Thank you for considering this suggestion.