There is some interesting discussion on ELU meta on what the difference is:
ELU is a site intended for "serious linguists." Over time, many non-native speakers stumbled across ELU, and would ask questions that native speakers considered very basic. This caused mixed feelings: on one hand, as the board became flooded with more and more basic and trivial questions, some users got discouraged or bored. On the other hand, no one really wanted to tell these English language learners, who were asking legitimate questions for a non-native speaker, that their questions were either not valid or not welcome.
On JLSE, I feel we certainly have both types of questions. Ones that more-or-less any fluent speaker could answer, and ones which even well-read native speakers would have a hard time answering without significant research.
If we are interested in attracting more native & fluent Japanese speakers to the site, I think it is highly worth our time to try and organize our questions so that they can easily find ones that are interesting to them.
Of course, the major complication is that this would be a completely subjective tag, unlike pretty much all of our other tags. But I think it can work — ELU and ELL seem to be functioning, after all, despite the same subjective call needing to be made — and I see very little downside risk in trying it out. At worst, the tag becomes useless and we remove it.
What do folks think about this? Is a tag the right technology for this? Are there any hidden downsides?