The issue of whether headlines and "headlinese" is on-topic came up because of the question We The People Petition on. I have to admit that I don't think it was a great question and that I'm a little conflicted about whether analyzing the grammar and vocabulary in a headline is something that would be a good use of the community's time.
On one hand, news headlines and news articles are, in my opinion, important for English learners to be able to understand and I think they are common sources for questions likely to get asked. On the other hand, headlines by their very nature are non-standard English. They aren't complete sentences, the language is contorted to be overly concise, and there's a huge dollop of idiom and wordplay thrown in to grab the native speaker's attention.
I feel that they are on-topic under the "Practical problems you encounter while learning English" part of the "What topics can I ask about here?". I think there is some value to helping learners decipher headlines and understand what parts of them aren't standard English because a grammar reference or dictionary isn't going to be that helpful. I do think though that the question I linked above had way too much abstract discussion to keep it squarely in the "practical problem" category, so I don't think that's the question I would hold up as the shining example of when a headline would be on-topic.
What do y'all think?